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Variation and natural selection in a population of sticklebacks Gasterosteus MacLean, James Alexander 1974

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VARIATION AND NATURAL SELECTION IN A POPULATION OF STICKLEBACKS (Gasterosteus). by James Alexander MacLean B.Sc, University of Manitoba, 1966 M.Sc., University of Manitoba, 1969 A thesis submitted i n p a r t i a l fulfilment of the requirements for the degree of Doctor of Philosophy In the Department of * Zoology We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July 191b In presenting th is thes is in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ibrary shal l make it f ree ly ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of th is thes is for scho la r ly purposes may be granted by the Head of my Department or by h is representat ives . It is understood that copying or pub l ica t ion of th is thes is fo r f inanc ia l gain sha l l not be allowed without my wri t ten permission. Department of The Univers i ty of B r i t i s h Columbia Vancouver 8, Canada i i ABSTRACT Threespine sticklebacks are genetically polymorphic for the number and arrangement of bony plates on the sides of the body. The adaptive significance and maintenance of plate variation was investigated i n Heisholt Lake, a small B r i t i s h Columbia lake with two separate basins. The population contains the low plated, p a r t i a l l y plated, and completely plated freshwater morphs of threespine sticklebacks, and plate number varies considerably within morphs. Frequencies of the plate phenotypes changed in space and time. Morph frequencies change spatially both between depths within an area, owing to segregation of breeding females, and between areas at the same depth. Phenotypic frequencies changed temporally both within and between generations. Phenotypes favored within a generation also increased in frequency from that generation to the next. At most stations in basin 1, low and completely plated sticklebacks increased,and p a r t i a l l y plated sticklebacks decreased in frequency both within and between generations. In basin 2, p a r t i a l l y plated sticklebacks were favored at many stations both within and between generations. Extreme phenotypes within a l l morphs increased i n frequency both within and between generations, and asymmetrical disruptive selection acted during at least one generation within a l l morphs. Interactions between genetic variation and structure of the st i c k l e -back population appear to explain changes in the frequency j f phenotypes in both space and time. Experiments to investigate the movement pattern of sticklebacks in Heisholt Lake show that the population i s composed of i i i resident individuals, which remain in a restricted area and maintain either a feeding or "breeding territory, and non-residents, which move from area to area and do not breed. The phenotype of an individual influences i t s chances to become a resident. Low and completely plated sticklebacks were favored in competition for territories in basin 1, but partially plated sticklebacks were often favored in basin 2.) Females with extreme phenotypes had the greatest chance of breeding, and asymmetrical disruptive selection acted within a l l morphs. The phenotype of a stickleback also influences i t s chances of being infected with Schistocephalus solidus, a cestode parasite that reduces the chances of infected sticklebacks to survive and reproduce. Partially plated sticklebacks had the.highest rate of infection in basin 1, but had the lowest rate of infection in basin 2 • Differential infection of phenotypes was at least part of the explanation for the observed temporal changes in phenotypic frequencies. Spatial changes in phenotypic frequencies are caused by changes in space in the results of competition for terr i t o r i e s . Temporal changes in phenotypic frequencies are explained by differential survival and reproduction of phenotypes as a result of differences between phenotypes in chancegto obtain a territory. i v TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i v LIST OF TABLES v i LIST OF FIGURES v i i ACKNOWLEDGEMENTS v i i i INTRODUCTION 1 MATERIALS AND METHODS 7 A. Study Area 7 B. Variation i n Sticklebacks 7 C. Collecting Sticklebacks 9 DISTRIBUTION OF STICKLEBACKS 10 A. Combining Samples from Successive Days 11 B. Morph Frequency and Depth 12 C. Morph Frequency and Area 17 D. Summary 19 ABUNDANCE OF STICKLEBACKS 19 VARIATION OF STICKLEBACKS 21 A. Between Morph Comparisons ••• 21 (1) Changes in Morph Frequency from May to September 21 (2) Changes i n Morph Frequency from Year to Year 27 B. Within Morph Comparisons 32; (1) Changes in Frequencies of Plate Number Phenotypes from May to September • 3L (2) Changes i n Frequencies of Plate Number Phenotypes from Year to Year 3I+ C. Summary I4.3 V Page STICKLEBACKS AND SCHISTOCEPHALUS SOLIDUS 45 MOVEMENTS OF STICKLEBACKS 49 A. Movement Patterns ..... , 49 B. Relative Numbers of Residents and Non-residents. 53 C. Summary ..... 57 VARIATION OF RESIDENT AND NON-RESIDENT STICKLEBACKS 5 7 A. Nesting Males .. 59 B. Breeding Females 66 C. Residents and Non-residents i n September 70 D. Summary 70 SUMMARY OF RESULTS 73 A. Changes in the Frequency of Phenotypes 73 B. Explanation of Observed Changes 74 DISCUSSION • 75 A. Behavior and Movement of Sticklebacks 75 B. Physiological Variation in Gasterp,steus aculeatus 81 C. Variation i n Resident and Non-resident Sticklebacks 83 BIBLIOGRAPHY ' 88 APPENDICES .. 97 fe TABLE LIST OF TABLES • p a g e I Morph f requencies o f s t i c k l e b a c k s caught i n an area o f b a s i n 2 on success ive days i n May 1970 . . . . 13 II Morph f requencies o f s t i c k l e b a c k s at d i f f e r e n t depths i n one a r e a , 1970 14 . I l l Morph f requencies o f s t i c k l e b a c k s at 10 s t a t i o n s i n b a s i n 2 i n He isho l t Lake i n May 1970 18 IV Summary o f Chi -squared t e s t s o f a s s o c i a t i o n between morph f requenc ies and s t a t i o n i n He isho l t Lake 1971-1973 19 a V Summary o f t e s t s of homogeneity and morph frequencies o f s t i c k l e b a c k s at a s t a t i o n ^ i n May and September 1971 and 1972 • • • 24 VT Re la t i ve f i t n e s s of p l a t e morphs o f .s t ick lebacks from May to September at s t a t i o n s i n Bas in 1 i n 1971 and 1972 26 VII R e l a t i v e f i t n e s s of p l a t e morphs o f s t i c k l e b a c k s from May to September at s t a t i o n s i n b a s i n 2 i n 1971-1972 29 VIII Summary o f t e s t s o f homogeneity o f f requencies o f p la t e morphs i n May o f 1971, 1972 and 1973 31 IX Summary of t e s t s of homogeneity o f p l a t e number f requencies w i t h i n morphs i n May and September o f 1971 and 1972 35 X Summary o f t e s t s of homogeneity of f requencies o f p l a t e number phenotypes w i th in morphs from May o f one year to May o f the f o l l o w i n g year 41 XI Propor t ion o f s t i c k l e b a c k s wi th d i f f e r e n t p l a t e morphs i n f e c t e d wi th Schis tocephalus s o l i d u s i n He isho l t Lake , June 1971 48 XII • Frequencies of marked and non-marked s t i c k l e b a c k s i n an area i n b a s i n 2 i n May 1972 56 XIII R e l a t i v e f i t n e s s o f marks wi th d i f f e r e n t p la t e morphs breeding i n b a s i n 1 6l XIV R e l a t i v e f i t n e s s o f males wi th d i f f e r e n t p l a t e morphs breeding i n b a s i n 2 , 1973 62 XV Summary of t e s t s o f homogeneity o f morph f requencies o f nes t ing males at d i f f e r e n t s t a t i o n s 63 XVI Summary of t e s t s o f a s s o c i a t i o n between the p l a t e morph o f female s t i c k l e b a c k s and breeding c o n d i t i o n 64 XVII Morph f requencies o f breeding and non-breeding female s t i c k l e b a c k s and r e l a t i v e f i t n e s s o f morphs i n e a r l y May i n He isho l t Lake 1971-1973 65 XVIII Morph f requencies o f res iden t and non-res ident s t i ck lebacks i n b a s i n 1 i n August 1972 71 v i i LIST OF FIGURES FIGURE Page 1 P la te morphs of s t i c k l e b a c k s i n - H e i s h o l t Lake . . . . . 3 a 2 He isho l t Lake on Texada I s l a n d , B r i t i s h Columbia, showing l o c a t i o n o f sampling s t a t i o n s 8 3 Depth d i s t r i b u t i o n of s t i c k l e b a c k s i n b a s i n 2 of He isho l t Lake , 1970 15 4 Depth d i s t r i b u t i o n of breeding female s t i c k l e b a c k s wi th d i f f e r i n g p l a t e phenotypes i n H e i s h o l t Lake i n June 1970 l6 5 Average catch per un i t e f f o r t (average o f s t i c k l e b a c k s / t r a p ) i n bas ins o f He isho i t Lake i n May and September, 1970-1973 22 6 Comparison o f f requencies o f p l a t e morphs o f s t i c k l e b a c k s at s t a t i o n s i n b a s i n 1 i n May and September o f 1971 and 1972 25 7 Comparison of f requencies o f p l a t e morphs o f s t i c k l e b a c k s at s t a t i o n s i n b a s i n 2 i n May and September o f 1971 and 1972 28 8 Comparison of f requencies of p l a t e morphs o f s t i c k l e b a c k s at s t a t i o n s i n b a s i n 1 i n May o f one year and May o f the f o l l o w i n g year " 32 9 Comparison o f f requencies o f p la te morphs o f s t i c k l e b a c k s at s t a t i o n s i n b a s i n 2 i n May of" one year and May o f the fo l lowing year 33 10 R e l a t i v e f i t n e s s and p l a t e number phenotypes w i th in morphs: from May to September 1971 (0) and 1972 (©) i n b a s i n 1 36 11 R e l a t i v e f i t n e s s of p l a t e number phenotypes w i t h i n morphs from May to September 1971 (0) and 1972 (©) i n b a s i n 2 38 12 R e l a t i v e change o f frequency of p l a t e number phenotypes w i t h i n morphs from May i n one year to May i n the f o l l o w i n g year i n b a s i n 1 40 13 ' R e l a t i v e change o f frequency o f p l a t e number phenotypes w i t h i n morphs from May i n one year to May i n the f o l l o w i n g year i n b a s i n 2 44 14 Rate o f i n f e c t i o n of s t i c k l e b a c k s wi th Schistocephalus s o l i d u s i n b a s i n 2 dur ing 1970 46 15 Sketch o f U-shaped bay (S ta t ion 26) i n b a s i n 2 used f o r experiment on movement pat terns of s t i c k l e b a c k s showing s i t e s at which t raps were set 51 16 Frequency o f marked s t i c k l e b a c k s at d i f f e r e n t d is tances from re lease area i n May and September 1971 52 17 Movement o f res ident and non- res ident s t i c k l e b a c k s from re lease area i n May, 1972 54 18 R e l a t i o n s h i p between dens i ty o f s t i c k l e b a c k s ( c a t c h / u n i t e f f o r t ) i n re lease area on day one and the propor t ion o f s t i c k l e b a c k s wi th t e r r i t o r i e s (frequency o f marked s t i c k l e b a c k s i n r e l e a s e area) i n re lease area on day one 58 19 R e l a t i v e f i t n e s s o f p l a t e phenotypes o f female s t i c k l e b a c k s i n b a s i n 1... 66 20 R e l a t i v e f i t n e s s o f p l a t e phenotypes o f female s t i c k l e b a c k s i n b a s i n 2... 68 21 The r e l a t i o n s h i p between dens i ty of s t i c k l e b a c k s i n a t r a p and the r e l a t i v e frequency of the p a r t i a l l y p la ted morph i n the breeding females caught i n the t rap - 1972.... 69 v i i i ACKNOWLEDGEMENTS Numerous people on Texada Island contributed to this research through their hospitality and assistance with the f i e l d work, but I would particularly l i k e to thank Mr. M. Pero, Ron and Darlene Arnold, John and Jacqueline Sellinten, and Don Wise. I am also grateful to many members of the Institute of Animal Resource Ecology, who listened patiently to various ramblings about sticklebacks in Heisholt Lake. I thank Steven Stearns, and Drs. D. Chitty, J. Myers, and A. Bir d s a l l for reading the manuscript and making many useful suggestions. I am indebted to Dr. Douglas Hay for the numerous stimulating discussions we had about sticklebacks, research, and where he/I was mistaken. I am particularly grateful to Dr. J.D. McPhail, my thesis supervisor, for his constant enthusiasm for discussion and research and his interest in my work. FROM THE NORTHERN WHIG AND BELFAST POST: MAY 30, 1928. 'Dozens o f t i n y red f i s h were found on the r o o f o f "a bungalow on the farm o f Mr. James McMaster, Drumhirk, near Comber, and on the ground i n the v i c i n i t y yesterday morning, and the ex t raord inary occurrence caused cons iderab le s p e c u l a t i o n . In the course o f enqu i r ies i t was ascer ta ined that j u s t be fore the d iscovery o f the f i s h there had been an e x c e p t i o n a l l y v i o l e n t thunderstorm with heavy r a i n . There i s no r i v e r i n the neighbour-hood, the nearest sheet o f water be ing S t r a n g f o r d -hough, two m i l e s d i s t a n t , and the theory advanced by an expert was 1 Adapted from Norman, J . R . and P. H. Greenwood. 1963. A H i s t o r y o f F i s h e s . Ernest Benn L t d . London 398p. INTRODUCTION ^ Population biologists are currently interested i n interactions between genetic variation and ecology, and particularly i n questions about the adap-tive significance and maintenance of variation in natural populations. While population geneticists and ecologists agree that a union between their disciplines is necessary to answer these questions, few actual attempts at such a union are made (Sheppard, 1969). This thesis investigates the adap-tive significance and maintenance of variation in later a l plate number i n threespine sticklebacks (Gasterosteus aculeatus L.). Sticklebacks are ideal animals for the study of selection and evolution in natural populations. They are abundant, easy to catch, and small enough to be observed and experimented with i n the f i e l d and laboratory. The biology of sticklebacks is well studied, although their ecology is relatively unknown. Marine and freshwater populations of threespine sticklebacks occur i n Europe, Asia, and North America. Marine populations appear to be pelagic and feed on plankton. Freshwater populations occur in; streams and lakes, and may be either pelagic or benthic feeders (Larson, 1972). Freshwater individuals mature in their f i r s t or second year, and l i v e for a maximum of three years; marine individuals mature i n one year, and seldom breed a second year (McPhail and Lindsey, 1970). Breeding behavior i s described by Tinbergen (l95l) and van den Assem (1967). Sticklebacks are extremely variable, showing polymorphic and polygenic morphological variation that can be scored or measured easily. Their short generation time in the laboratory f a c i l i t a t e s analysis of the inheritance of this variation. This study i s one of a series on the adaptive significance and mainten-ance of variation in populations of sticklebacks. The polymorphism for number and arrangement of bony ,plates on the sides of the body has attracted considerable attention (Bertin, 1925; Heuts, 1947a; Lindsey, 1962; Munzing, 1963; Hagen, 1967). Unfortunately, this attention has produced a state of advanced confusion, so I w i l l b r i e f l y .describe the variation in l a t e r a l plates and summarize previous results of studies on inheritance and maintenance of this variation. Bertin (1925) and Heuts (1947a) described two morphs of threespine stickleback: (1) a large, silvery, marine morph, with relatively high numbers of plates and g i l l rakers; (2) a small, drab green, freshwater morph, with fewer plates and g i l l rakers. The marine morph is anadromous and breeds i n freshwater, and hybrids between the morphs are found i n areas of sympatry. Munzing (1963) shows that this model does not adequately account for observed differences between European populations, and proposed three morphs of stickleback: (1) a completely plated morph, trachurus; (2) a morph with few plates, leiurus; (3) a morph with intermediate plate numbers, semiarmatus. He found anadromous populations with a l l three morphs; freshwater popula-tions of trachurus; populations with either leiurus and semiarmatus or 3 trachurus and semiarmatus which lack the third morph to explain the presence of intermediates; and pure populations of semiarmatus. Hagen and Gilbertson (l9T3a) argue that variation in freshwater and marine populations should be considered separately, and use the terms low plated, p a r t i a l l y plated, and completely plated for the freshwater morphs (Fig. l ) . Plate numbers vary considerably within morphs. Hay (1974) suggests that the pattern of plate variation i s as important as number of plates. Heuts (1947a) and Munzing (1963) proposed a genetic model with two major genes to explain segregation i n crosses between leiurus (low-plated) and trachurus. Hagen and Gilbertson (1973a) also found that freshwater morphs are determined by segregation of major genes, but that the simplest model to explain results of crosses involves two autosomal l o c i , each with two all e l e s . Lindsey (1962) and Hagen (1972) report high h e r i t a b i l i t i e s for plate numbers within a morph (0.50 to 0.84). Hagen and Gilbertson (1973a) suggest that variation within morphs results from segregation of polygenes. The central problem of ecological genetics of sticklebacks is to explain the variation in plate number within and between populations (Penczak, 19^5, 1966; Miller and Hubbs, 1969; Hagen and Gilbertson, 1972). Munzing (1963) proposed two hypotheses to explain the observed pattern of variation: (1) that leiurus and trachurus are morphs of a polymorphic species, implying that selection maintains variation; (2) that leiurus and trachurus were geographically isolated during the Pleistocene, so that the present pattern of variation is due to dispersal and subsequent introgression between these morphs. 3a FIG. 1: Plate Morphs of sticklebacks i n Heisholt Lake (From Hagen and Gilbertson, 1973a) 3 f t LOW PLATED MORPH PARTIALLY P L A T E D MORPH COMPLETELY PLATED MORPH Numerous studies show that selection acts on variation i n plate number. Heuts (1947b) shows that leiurus and trachurus are physiologically different, and suggests that these differences reduce gene flow through habitat selection. Plate number phenotypes within morphs are also associated with physiological differences (Heuts, 1947b; Lindsey, 1962). Hagen (1967) studied isolating mechanisms between marine anadromous trachurus and freshwater leiurus. Hybrids were confined to a narrow zone between the morphs. He found no behavioral or genetic barriers to hybridization, but that ecological isolation, involving numerous adaptations to different microhabitats, reduced gene flow between morphs. Hay (1969) found p a r t i a l ethological isolation between morphs, as Ford (1971) anticipated. Several studies demonstrate selective predation on sticklebacks favoring certain plate numbers (Moodie, 1972a; Hagen and Gilbertson, 1972, 1973b; Hay, 1974; Lea, 1969). Laboratory experi-ments designed to examine predation suggest that d i f f e r e n t i a l survival of phenotypes within morphs is due to behavioral differences (McPhail, 19&9; Moodie, McPhail and Hagen, 1973). Males with a particular plate count build nests in micro-habitats that dif f e r from those chosen by other pheno-types (Moodie, 1972b; Hay, 1974; McPhail, pers, comm.). Plate phenotypes dif f e r i n fecundity of females (Hagen, 1967; Moodie, 1972b; Hay, 1974; McPhail, unpub. data). Although the adaptive significance of variation in plates is unknown, selection clearly acts on a variety of characters linked to plate number. Hybridization occurs between leiurus and trachurus, and no selective mechanism acting against semiarmatus i s known (Hay, 1974). Miller and Hubbs (1969) argue that introgression between leiurus and trachurus explains the observed geographical pattern of variation. While intorgression occurs in some areas, permanent sympatric populations of a l l three plate morphs 5 also occur (Hagen and Gilbertson, 1972^ suggesting that introgression does not necessarily lead to elimination of differences between morphs. Clearly, selection can maintain the morphs despite gene flow. Other morphological.characters of sticklebacks also vary within and between populations. Variation i n g i l l raker numbers is related to feeding strategies of a population (Larson, 1972; Hagen and Gilbertson, 1972), and he r i t a b i l i t y of g i l l raker number is high (0.58) (Hagen, 1972). Male sticklebacks vary i n breeding coloration, which is genetically inherited," and di f f e r e n t i a l predation of color morphs is a selective force maintaining variation (McPhail, 1969; Semler, 1972; Moodie, 1972b). McPhail (1969) showed that hybrid i n f e r i o r i t y i s also involved in maintenance of variation in breeding color. Other characters known to show adaptive patterns of variation include pelvic spine length (Hagen, 19^7; Moodie, 1972a), body size (Moodie, 1972b; Larson, 1972), and dorsal spine number (McPhail, pers. comm.) Until recently, biochemical variation i n sticklebacks has been ignored, but preliminary studies (Jones, pers. comm.; Kusa, 1966; Callegarini and Cucchi, 1969a, b) suggest that morphological and biochemical analyses could be profitably combined in the future. I was interested i n the adaptive significance of variation in plate number, and in how that variation is maintained in populations of sticklebacks. I followed the guidelines suggested by Ford (196U) to choose a suitable population for the study. He identifies four situations where evolution occurs fast enough to be studied: (l) when marked numerical fluctuations affect isolated populations; 6 (2) when polygenic characters are studied, either (a) i n populations inhabiting ecologically distinct and isolated areas •, or (b) even i n the absence of isolation i f subject to strong selective pressures', (3) i n a l l types of genetic polymorphism; (k) when a species spreads into a new area. Ford suggests that most changes i n this situation would be physiological f and d i f f i c u l t to study The stickleback population i n Heisholt Lake appeared to f u l f i l l several of the suggested c r i t e r i a . The lake was formed during the f a l l of 1966, and sticklebacks had been introduced i n May 1967- When the population was sampled i n May 1970,density was s t i l l very low, suggesting that population size would increase i n subsequent years. Also, the three freshwater morphs (low plated, p a r t i a l l y plated, and completely plated) were present i n the population. This situation offered a unique opportunity to study selection and evolution i n a natural population, and to investigate the adaptive sig-nificance and maintenance of plate variation of sticklebacks. My approach in th i s study was: (1) to describe spatial and temporal changes in frequencies of plate phenotypes; (2) to attempt to explain observed changes. . 7 MATERIALS AND METHODS A. Study Area Heisholt Lake is a small lake (0.5 km in length) on Texada Island i n Georgia Strait, B r i t i s h Columbia (Fig. 2). The lake formed when a lime-stone mine closed i n 1966, and the pit f i l l e d with water. The two basins of the lake are connected for one to two months each winter by a small, shallow stream flowing from basin 1 to basin 2. Shallow r i f f l e s and a rock dam prevent sticklebacks from moving between basins. No streams enter or leave the lake, but a spring flows into basin 1, and water seeps through sand and gravel into a marsh at the south end of basin 2. The limestone was removed i n f l a t shelves, and the bottom of the lake i s very f l a t (maximum depth 11 m). The rock is covered with 1-2 cm of marl, and Chara sp. grows abundantly in some areas. The local Fish and Game club introduced approximately 1000 threespine sticklebacks and several hundred coho salmon (Oncorhynchus keta) and rainbow trout (Salmo gairdneri) into each basin in May, 1967- The fis h were collected from Grilles Bay Creek,a small coastal stream on the island. Salmon are no longer found in the lake, but the trout have bred successfuly and are s t i l l present in small numbers. Salamanders (Tarica granulosa) are abundant i n the lake, par-t i c u l a r l y during spring, when they are breeding. B. Variation in Sticklebacks Preliminary sampling in May, 1970, showed that three plate morphs I 8 FIG. 2: Heisholt Lake on Texada Island, B r i t i s h Columbia, showing location of sampling stations. 9 are present in Heisholt Lake. These morphs di f f e r in plate number and pattern, but not in body size, color, and g i l l raker number. Hagen and Gilbertson (1973a) propose the following definitions of the freshwater plate morphs: (1) the low plated morph includes a l l individuals with only anterior plates (Fig. l ) . Plate numbers of sticklebacks of this morph vary from 3 to 17 in Heisholt Lake; (2) the p a r t i a l l y plated morph includes individuals with a gap between anterior plates and a caudal keel of plates. Plate numbers of sticklebacks of this morph vary from 7 to 29; (3) the completely plated morph includes a l l individuals with a continuous series of plates along the sides of the body. Plate numbers of sticklebacks of this morph vary from 28 to 36. Hagen and Gilbertson 1s terminology is used throughout this thesis. A l l three plate morphs are present i n Gilles Bay Creek. C. Collecting Sticklebacks Sticklebacks were collected with wire mesh minnow traps (No. 12562, Canada Fishing Tackle and Sports Ltd.). Stott (1970) discussed several problems associated with the use of unbaited f i s h traps, but the most serious criticism i s that the number of fis h caught i s dependent on the influence of environmental factors on activity levels. Sticklebacks were collected from 30 stations in the lake (Fig. l ) during the f i r s t two weeks of both May and September from 1971 to 1973. During each 10 sampling p e r i o d , two t raps were p laced on the bottom at e x a c t l y the same s i t e s a t . e a c h s t a t i o n , and s t i c k l e b a c k s were removed at the same time every day. I t r i e d to take equal numbers o f t r a p c o l l e c t i o n s at each s t a t i o n dur ing a sampling p e r i o d , but some t r a p s were moved or opened. Nest ing male s t i c k l e b a c k s were c o l l e c t e d wi th a d ipne t . S t i c k l e b a c k s were preserved i n 10$ f o r m a l i n , and l a t e r were counted and measured i n the l a b o r a t o r y . P l a t e number and morph, standard l e n g t h , sex , and g i l l raker number were recorded f o r each i n d i v i d u a l accord ing to c r i t e r i a d i s c u s s e d by Hagen and G i l b e r t s o n (1972). Numbers o f eggs i n r i p e females (those with ye l low eggs separated form whi te , undeveloped eggs i n the ovary) and the number o f Sch is tocepha lus s o l i d u s p l e r o c e r c o i d s were a lso counted. DISTRIBUTION OF STICKLEBACKS When I began t h i s s t u d y , I was p a r t i c u l a r l y i n t e r e s t e d i n i n t e r a c t i o n s between numbers o f s t i c k l e b a c k s and genet ic v a r i a t i o n i n the p o p u l a t i o n ; I intended t o f o l l o w changes i n popu la t ion s i z e and i n the f requencies o f phenotypes. I wanted to est imate p l a t e number f requencies by c o l l e c t i n g l a rge samples from s e v e r a l a r e a s , and to estimate popu la t ion s i z e wi th mar,k-recapture techn iques . These procedures assume tha t a l l i n d i v i d u a l s i n the popu la t ion are mixing randomly. During 1970,1 examined d i s t r i b u t i o n o f p l a t e phenotypes i n space to t e s t t h i s assumption i n H e i s h o l t Lake. Space i n a lake has both a h o r i z o n t a l and a v e r t i c a l component (area and depth) . To t e s t the assumption o f random m i x i n g , I asked two quest ions about the d i s t r i b u t i o n o f phenotypes : 11 (l) do relative frequencies of morphs change with depth within an area? Heuts (1947a) found that stickleback morphs have different temperatures for optimal survival of eggs to hatching, suggesting that adults are physio-l o g i c a l l y different. Since temperature varies with depth during a year, I predicted that physiological differences between morphs would be reflected in differences in distribution of phenotypes with depth; (2.) do morph frequencies at the same depth change from area to area? Frequencies of phenotypes in stickleback populations are usually estimated from large numbers of individuals collected i n a single area. This assumes that frequencies do not change between areas. When this assumption has been tested, no differences between areas were found (Moodie, 1972b; Hagen and Gilbertson, 1972; Hay, 1974), and I expected to find no differences i n Heisholt Lake. This section of the thesis presents results of tests of the assumption that sticklebacks assort randomly throughout a basin. A. Combining Samples from Successive Days A problem with answering questions about the distribution of phenotypes during 1970 was that few sticklebacks were caught in a 24 hr trap set. Samples were taken on several successive days and had to be combined for accurate estimates of morph frequencies. Sticklebacks were collected fnom a site in basin 2 for six successive days during May 1970 to test the assumption that morph frequencies; at a site do not change from day to day 12 (Table I ) . Morph frequencies did not change significantly from day to day 2 (chi-square test, X = 6.77, 10 d.f., p > 0.7), so samples taken on successive days were combined i n estimating morph frequencies. B. Morph Frequency and Depth Traps were set at 2 m intervals from 0 to 10 m in one area of basin 2 (near station 18) at four different times during 1970 to determine i f morph frequencies changed with depth (Table II). Equal numbers of samples were taken at a l l depths during each sampling period. The numbers of individuals caught at each depth shows that the depth distribution of sticklebacks changes during a year (Fig. 3). Sticklebacks are found i n shallow areas during early spring,but they move deeper in the lake during June and July. No preference for a particular depth is apparent i n August. Larson (1972) describes a similar seasonal pattern of distribu-tion of sticklebacks i n Paxton Lake on Texada island. J2. Morph frequencies changed with depth during June (chi-square test, X £ = 25.98, 8 d.f., p < 0.01), but i n May, July, and September, differences between depths were not significant. Differences between depths i n June appeared to be due to differences between morphs in the distribution of breeding females (Fig. 4). Females produce eggs from late A p r i l to mid-July i n Heisholt Lake. Ripe females of 13 TABLE I: Morph f requencies o f S t i c k l e b a c k s caught i n an area o f B a s i n 2 on success ive days i n May, 1970. C h i -square i s the r e s u l t of a t e s t o f a s s o c i a t i o n between morph f requencies and days. NUMBERS OF STICKLEBACKS DAY LOW PARTIALLY COMPLETELY PLATED ' PLATED PLATED 1 17 11 18 2 12 9 14 3 10 5 9 k 10 15 16 5 11 13 9 6 11 15 17 X 2 = 6.77, lOdf. , p>0.70 TABLE I I : 1 Morph frequencies of sticklebacks at different depths in one area, 1970. Chi-sguares are results of tests of association between morph frequencies and depth for each sampling period. Samples from 0 and 2 m in June were combined in calculation of Chi-square. NUMBERS OF STICKLEBACKS May 15-18 Depth .. (m. ) Low Plated June 15-18 July 15-19 August 23-25 Partial l y Completely Plated Plated Low Parti a l l y Completely Low Partially Completely Low Par t i a l l y Completely Plated Plated Plated Plated Plated Plated Plated Plated Plated 0 25 55 34 5 ) 4 9 6 7 12 " 9 2 5 5 7 3J 4 11 21 16 12 24 14 4 9 12 11 5 4 11 1 4 7 7 9 4 6 9 14 16 11 10 10 5 9 5 3 17 9 8 3 10 14 17 29- 12 8 36 28 11 20 18 10 2 15 13 5 14 12 8 39 29 13 16 8 X 2 = 12.35, lOcLX, p>0.25. X 2 = 25.98, 8<L£, p<0.01. x 2 = 9.61, 10 d£, P>0.25. X 2 = 8.85, 10 df„ ; 15 FIG. 3: Depth distribution of sticklebacks in Basin 2 of Heisholt Lake, 1970. Numbers i n brackets are the tot a l number of sticklebacks caught at a l l depths. F R E Q U E N C Y OF S T I C K L E B A C K S (%) cM 2.H 4-4 Q _ U J 6-J 8. IO 20 30 40 50 O IO 20 30 40 O 10 20 30 40 O IO 20 30 40 J I l J 1 1 1 1 L ! 1 1 MAY ( 2 5 9 ) JUNE O6O) JULY ( 2 4 6 ) AUGUST (213) 1 j 16 FIG. k: Depth distrihution of breeding female sticklebacks with differing plate phenotypes in Heisholt Lake in June, 1970. Numbers in brackets are the tot a l number of females of each morph. F R E Q U E N C Y OF S T I C K L E B A C K S (%) i 17 a l l morphs were found at only 0 and 2 m depths in early May, but they move into deeper areas as the breeding season continues. In June, low plated females are found i n shallow areas and completely plated females i n deep areas, while p a r t i a l l y plated females are caught at a narrow range of depths between the other morphs. This seasonal distribution pattern suggests that breeding females are not cueing on depth, but on an environmental factor, perhaps temperature, that changes seasonally at a given depth. Male sticklebacks were breeding at depths from 0 to 8 m in late June, 1971, so the depth at which a female lays her eggs may be influenced by her phenotype. The prediction that morph frequencies would change with depth was true only in June, when segregation of breeding females occurs. Differences i n the depth distribution of morphs does not occur at other times of the year. This result means that morph frequencies can only be estimated accurately either in early spring or after breeding ceases. C. Morph Frequency and Area Sticklebacks were collected at a depth of 3 m at 10 stations in basin 2 during May, to determine i f morph frequencies of sticklebacks change between areas (Table III). Two traps were set at each station and sticklebacks were removed for five days. Morph frequencies differed between stations (chi-square test, 2 X = 113.34, 18 d.f., p * 0.001), indicating that sticklebacks do not move randomly throughout a basin in Heisholt Lake. Clearly, my original conception of the structure of stickleback populations was wrong, and I 1 18 TABLE III: Morph frequencies of sticklebacks at 10 stations i n Basin 2 of Heisholt Lake i n May, 1970. Chi-squared i s result of a test of association between morph frequencies and sampling areas. NUMBERS OF STICKLEBACKS PARTIALLY COMPLETELY PLATED PLATED 1 70 66 86 2 60 112 81 3 44 103 51 4 23 22 18 5 70 60 75 6 43 21 32 7 12 47 30 8 32 43 17 9 38 45 33 10 55 11 30 X 2 = 113.84, 18 df., p>0.01 A T , ™ LOW PLATED 19 could not estimate either morph frequencies with large samples from one area or population size with mark-recapture techniques. From 1971 to 1973, sticklebacks were collected at 15 stations in each basin i n both May and September. Morph frequencies (Appendix A) did not dif f e r between stations in a l l sampling periods (Table IV). Also, differences between stations were not significant at the same time in both basins. These results w i l l be discussed again later, but they do not alter the conclusion that sticklebacks do not mix randomly within a basin. D. Summary The plate phenotype of a stickleback influences i t s distribution in space. Morph frequencies change with depth owing to segregation of breeding females. Morph frequencies also change from area to area within a basin, although differences between areas are not always significant. ABUNDANCE OF STICKLEBACKS Low stickleback densities during May, 1970, suggested that population size would continue to increase during this study. I was interested in following changes in the numbers 6"f sticklebacks because density might be important in explaining observed changes i n frequencies of phenotypes with time. However, sticklebacks do not mix randomly in a basin, and therefore mark-recapture techniques could not be used to estimate numbers of sticklebacks. TABLE IV: Summary of Chx-squared tests of association between morph frequencies and station i n Heisholt Lake, 1971-1973 (See Appendix A). DATE BASIN xf cLf pi May 1971 Sept 1971 May 1972 Sept 1972 May 1973 r, 2 1 2 1 2 1 2 1 2 30.28 32.96 29.83 37.11 42.83 30.83 47.86 28.39 36.40 38.67 28 28 28 28 28 28 28 24 28 28 > 0.25 > 0.10 > 0.25 > 0.10 < 0.05 > 0.25 < 0.025 > 0.25 > 0.10 > 0.10 20 Instead, catch per unit effort was used to follow changes in population" size. The number of sticklebacks in each trap was recorded during May and September from 1971 to 1973, and average number of sticklebacks per trap was calculated for each basin (Appendix B). Catch per unit effort was also estimated for 1970 from a l l samples collected i n both basins i n May and September. Sticklebacks breed from May to mid-July in Heisholt Lake, and small numbers of young sticklebacks are f i r s t caught in traps during September. The young continue to grow in size throughout the winter, and almost a l l can be caught in traps during May. The average number of sticklebacks per trap increased each May from 1970 to 1973 (Fig. 5), which suggests that population size increased each year throughout the study. The rate of increase appears sli g h t l y higher in basin 2, but the numbers of sticklebacks per trap varied considerably from station to station because of the clumped distribution of sticklebacks, so that differences between basins probably reflect the stations chosen rather" than real differences in population size. Large numbers of sticklebacks die each year between May and September. Length frequency analysis i n May shows that only 1-2% of the breeding population survives for more than one year. Number of sticklebacks per trap in September did not increase from year to year, so a larger propor-tion of the population died between May and September each year from 1971 to 1973. 21 Summary in Mau The number of sticklebacks in Heisholt Lake increased,eacti year during the study. Most individuals l i v e less than one year, so that the proportion the population that died between May and September increased each year. VARIATION OF STICKLEBACKS I asked two questions about changes in frequencies of plate phenotypes with time: (1) do phenotypic frequencies change from May to September (within generations)? Large numbers of sticklebacks die each year between May and September, and I was interested in determining i f di f f e r e n t i a l mortality of phenotypes occurs; (2) do phenotypic frequencies change from year to year (generation to generation)? I was particularly interested in interactions between genetic variation and population size. Sticklebacks were collected from 30 stations in both May and September each year. Frequencies of morphs and plate numbers were compared within and between years to determine i f temporal changes occurred. This section of the thesis presents results of these comparisons. A. Between Morph Comparisons (l) Changes in morph frequency from May to September. Morph frequencies in May and September at each station were compared to determine i f natural selection acts on morph frequencies during a generation. The number of sticklebacks trapped during September, 1973, was too small to estimate morph frequencies. 22 FIG. 5: Average catch per u n i t e f f o r t (average number of s t i c k l e b a c k s / t r a p ) i n bas ins of He isho l t Lake i n May and September, 1970-1973. 22a I 1 1 1 1970 1971 1972 1973 Y E A R 23 Differential mortality of morphs occurred at::;mQst stations in basin 1 during 1971 and 1972, but in both years changes were significant at only a few stations i n basin 2 (Table V). Two techniques were used to examine patterns of selection: (1) For each morph I plotted frequency in May against frequency in September at each station,to examine the direction of change in frequencies of a morph within a basin; (2) I calculated relative fitness of morphs from frequencies i n May and September at each station to compare the chances of morphs to survive in different areas of the lake. Relative fitness, defined as the prob-a b i l i t y of survival from May to September, was calculated as suggested by O'Donald (1968, 1970). Hagen and Gilbertson (1973b) discuss some problems in interpreting relative fitnesses of sticklebacks. The pattern of selection was similar at most stations in basin 1 during both 1971 and 1972 (Fig. 6). The frequency of low plated sticklebacks increased and decreased at an equal number of stations in 1971, and increased at most stations i n 1972. The frequency of pa r t i a l l y plated individuals decreased, and completely plated sticklebacks increased i n frequency at most stations i n both years. Relative fitnesses of morphs show that completely plated sticklebacks were favored at lb of the 15 stations in basin 1 during 1971 (Table VI). P a r t i a l l y plated individuals had the lowest fitness at most stations and the fitness of low plated sticklebacks was generally intermediate. Pa r t i a l l y plated sticklebacks were again selected against at a l l stations i n 1972, but the favored morph changed from station to station. Low plated sticklebacks were favored at stations 4, 5, 6, 7> and 9 i n adjacent areas of TABLE V: Summary of tests of homogeneity of morph frequencies of sticklebacks at a station in May and September, 1971 and 1972. BASIN 1 BASIN 2 1971 1972 1971 1972 Station X X Station X 1 4.43 > 0.10 5.10 > 0.05 16 7.42 < 0.025 1.99 > 0.25 2 4.02 > 0.10 6.35 < 0.05 17 0.58 > 0.50 8.01 0.025 3 7.03 < 0.05 4.43 > 0.10 18 4.02 > 0.10 0. 54 > 0.75 4 . ,8.54 < 0.025 5.15 > 0.05 19 2.31 > 0.25 1.52 > 0.25 5 8.62 < 0.025 13.43 < 0.005 20 0.91 > 0.50 0.41 > 0.75 6 3.04 > 0.10 6.74 < 0.05 21 3.06 > 0.10 -7 31.14 < 0.005 20.45 < 0.005 22 2.37 > 0.25 7.19 < 0.05 8 5.52 > 0.05 17.00 < 0.005 23 5.58 > 0.05 -9 15.49 < 0.005 9.60 < 0.01 24 2.10 > 0.25 0.91 > 0.50 10 6.17 < 0.05 18.28 < 0.005 .25 0.27 > 0.75 2.98 > 0.10 11 10.80 < 0.005 13.69 < 0.005 26 2.60 > 0.25 2.53 > 0.25 12 1.87 > 0.25 7.73 < 0.025 27 4.83 > 0.05 0.83 > 0.50 13 2.46 > 0.25 4.04 > 0.10 28 3.14 > 0.10 2.21 > 0.25 14 8.15 < 0.025 24.63 < 0.005 29 1.09 > 0.50 1.41 > 0.25 15 3.36 > .0.10 4.39 >0.10 30 1.44 > 0.25 7-73 < 0.025 FIG. 6: Comparison of frequencies of plate morphs of sticklebacks at stations in Basin 1 in May and September of 1971 and 1972. F R E Q U E N C Y IN M A Y (%) TABLE VT: Relative fitness of plate morphs of sticklebacks from May to September at stations in Basin 1 i n 1971 and 1972. RELATIVE FITNESS  1971 1972  STATION LOW PARTIALLY COMPLETELY LOW PARTIALLY COMPLETELY PLATED PLATED PLATED PLATED PLATED PLATED 1 0.76 0.31 1 0.89 0.34 1 2 0.59 0.46 1 0.59 0.39 - 1 3 0.38 0.33 1 0.30 0.33 1 4 0.72 0.27 1 1 0.36 0.73 5 0.46 0.31 1 l 0.24 0.99 6 O.80 0.40 1 1 0.14 0.68 7 O.16 0.16 1 1 0.15 0.75 8 0.45 O.58 1 0.35 0.13 1 9 0.30 0.20 1 1 0.34 0.82 10 0.93 0.54 1 0.87 0.11 1 11 0.68 0.32 1 0.74 0.29 1 12 1 0.81 0.44 1 0.27 0.46 13 0.50 0.31 1 1 0.37 0.50 14 0.62 0.23 1 0.54 0.14 1 15 0.25 0.14 1 1 0.31 0.58 27 basin 1, and at stations 12, 13 and 15, which are also adjacent. Similarly, completely plated sticklebacks had the highest fitness i n large adjacent areas of the basin. The favored morph changed at 7 of the 15 stations from 1971 to 1972. Average relative fitness of p a r t i a l l y plated sticklebacks decreased from 0.35 i n 1971 to 0.26 i n 1972, suggesting that selection against this morph increased.-No general pattern of selection occurred throughout basin 2 in 1971 and 1972, as the direction and degree of changes i n relative frequency varied from station to station (Fig. 7). In contrast to basin" 1, p a r t i a l l y plated sticklebacks increased in frequency at a majority of stations i n basin 2 in both years. This suggests that p a r t i a l l y plated sticklebacks are not always selected against, as observations in basin 1 would suggest. Relative fitnesses of morphs varied greatly from station to station (Table VII), suggesting that chances for sticklebacks of a particular morph to survive vary in space. Spatial patterns of fitnesses, similar to those observed in basin 1, are also apparent i n basin 2, Fitness of p a r t i a l l y plated sticklebacks was high at stations 16, 17, 18, 19, and 24, and lower at stations 20, 21, 22, and 23 in both 1971 and 1972, suggesting that i n both years chances for a morph to survive were similar i n large adjacent areas of the basin. The favored morph changed from 1971 to 1972 at 8 of 13 stations, suggesting that the selective environment for plate morphs of sticklebacks changes i n both space and time in basin 2. (2) Changes in morph frequency from year to year. Morph frequencies i n May of 1971, 1972, and 1973 were compared to 28 FIG. 7: Comparison of frequencies of plate morphs of sticklebacks at stations in basin 2 in May and September of 1971 and 1972. 28a 1972 FREQUENCY IN MAY (%) TABLE VTI : Relative fitness of plate morphs of sticklebacks from May to September at stations in basin 2 in 1971 and 1972. RELATIVE FITNESS  1971 1972 STATION LOW PARTIALLY COMPLETELY LOW PARTIALLY COMPLETELY PLATED PLATED PLATED PLATED PLATED PLATED 16 0.35 1 0.72 1 0.98 0 .64 17 0.70 1 0.86 0.61 1 0.08 18 0.37 1 0.50 0.74 1 0.82 19 0.20 0.96 l 0.75 1 0.57 20 0.78 0.68 l 1 0.81 0.95 21 1 0.86 0.41 - - -22 o.4o O.62 1 0.40 0.20 1 23 0.36 0.25 1 - - -2k 0.48 l 0.56 o.4o 1 1 25 1 0.79 0.70 1 0.37 0.56 26 1 0.81 0.38 1 0.32 0.57 27 1 0.83 0.32. 0.65 0.96 1 28 0.37 0.54 1 1 0.22 0.59 29 1 0.54 0.51 0.47 0.80 1 30 0.6o O.78 1 0.29 0.58 1 30 determine i f relative frequencies of morphs change from year to year. Morph frequencies changed between years at 9 of the 30 stations (Table VIII). Frequency of a morph i n May was plotted against i t s frequency the following May to examine patterns of change i n morph frequencies from year to year. At most stations in basin 1, low and completely plated sticklebacks increased in frequency from 1971 to 1972 and from 1972 to 1973, while p a r t i a l l y plated individuals decreased. (Fig. 8) This pattern of change in morph frequency from year to year is similar to the pattern of change from May to September. Low and completely plated sticklebacks increased in frequency and p a r t i a l l y plated individuals decreased both within and between years in basin 1 throughout the study. Frequency of pa r t i a l l y plated sticklebacks increased and low and completely plated sticklebacks decreased in frequency from 1971 to 1972 at most stations ihi/basin 2. (Fig. 9) This pattern of change was reversed from 1972 to 1973, as low and pa r t i a l l y plated individuals increased and pa r t i a l l y plated individuals decreased in frequency at most stations, although changes in frequency of the completely plated morph were small. In both basins, the direction of change in the frequency of low and completely plated sticklebacks was identical and inversely related to the direction of change i n frequency of p a r t i a l l y plated sticklebacks. Changes in frequencies within and between years again appeared to be related in basin 2. Partially plated sticklebacks increased in frequency at most stations during 1971 and from 1971 to 1972. TABLE VIII: Summary of tests of homogeneity of frequencies of plate morphs in May of 1971, 1972, and 1973. BASIN 1 BASIN 2 STATION STATION 1 2.45 > 0.50 16 16.60 < 0.005 2 4.99 > 0.25 17 4.06 > 0.25 3 4.81 > 0.25 18 8.13 > 0.05 4 3.50 > 0.25 19 5.85 > 0.10 5 3.10 > 0-50 20 4.21 > 0.25 6 2.81 > 0.50 21 2.15 > 0.50 7 13.74 < 0.01 22 18.04 < 0.005 8 3.77 > 0.25 23 3.25 > 0.50 9 17.28 < 0.005 24 3.71 > 0.25 10 11.45 < 0.025 25 0.88 > 0.90 11 12.56 < 0.025 26 7.84 > 0.05 12 10.24 < 0.05 27 7.45 > 0.05 13 5.43 > 0.10 28 5.58 > 0.10 Ik 15.35 < 0.005 29 3.36 > 0.50 15 22.76 < 0.005 30 6.87 > 0.10 32 FIG; 8: Comparison of frequencies of plate morphs of sticklebacks at stations in basin 1 in May of one year and May of the following year. 32a FREQUENCY IN MAY - Y E A R 1 (%) 33 FIG. 9: Comparison of frequencies of plate morphs of sticklebacks at stations in basin 2 i n May of one year and May of the following year. F R E Q U E N C Y IN M A Y - Y E A R 1 34 B. Within Morph Comparisons (l) Changes in frequencies of plate number phenotypes from May to September. Frequencies of plate number phenotypes within a morph were estimated for each basin i n May and September from 1971 to 1973. Samples from a l l stations i n a basin were combined to reduce sampling errors i n estimating frequencies. This assumes that plate number frequencies do not change from area to area i n a basin. Interpretation of changes in frequencies within and between years must recognize the p o s s i b i l i t y that observed changes are due to differences between areas. Frequencies of plate number phenotypes in May and September weiee compared to determine i f natural selection acts within generations on variation i n plate number within morphs (Appendix C). Differential mortality of plate number phenotypes occurred within the low and p a r t i a l l y plated morphs in basin 1 in both 1971 and 1972, and within the low and completely plated morphs in basin 2 during 1971 (Table IX). Other changes i n relative frequency of plate number frequencies within morphs were not significant. Relative fitnesses of plate number phenotypes within morphs were calculated to examine patterns of selection. In basin 1, disruptive selection favc-vd individuals within the low plated morph with extreme plate numbers i n both 1971 and 1972 (Fig. 10). This disruptive selection also had a directional component, as 9 - to 17 - plated individuals had a selective advantage over 3~to 4-plated sticklebacks in both years. TABLE IX: Summary of tests of homogeneity of plate number frequencies within morphs in May and September of 1971 and 1972. BASIN YEAR PLATE MORPH tf2 &£ 1 1971 Low plated 34.72 5 < 0.005 P a r t i a l l y plated 26.37 6 < 0.005 Completely plated 3.84 5 > 0.50 1972 Low plated 95.23 5 < 0.005 P a r t i a l l y plated 16.84 6 < 0.01 Completely plated 2.94 5 > 0.50 1971 Low plated 17.18 5 < 0.005 P a r t i a l l y plated 8.49 6 > 0.10 Completely plated 23.57 5 < 0.005 1972 Low plated 2.94 5 > 0.50 Partially plated 7.62 6 > 0.25 Completely plated 4.71 5 > 0.25 36 FIG. 10: Relative fitness of plate number phenotypes within morphs from May to September, 1971 (0) and 1972 (©) i n Basin 1. P L A T E N U M B E R 37 Thoday (1972) uses the term asymmetrical disruptive selection for this pattern of fitnesses. Asymmetrical disruptive selection also occurred within the completely plated morph during both years. The favored phenotype had 33 plates in 1971,and 28 to 29 plates in 1972. No specific pattern of selection occurred within the pa r t i a l l y plated morph i n either 1971 or 1972, although fitnesses of phenotypes were similar i n both years. In basin 2, directional selection favored 3-to 4-plated sticklebacks within the low plated morph during 1971 (Fig. 11). The favored phenotype in 1972 was again 3-to 4-plated, but selection was disruptive, as 7-plated sticklebacks had a higher fitness than 5-, 6-, and 8-plated individuals. Disruptive selection favored extreme plate numbers within the completely plated morph in both years. The favored phenotype within the completely plated morph was similar, in both basins, as 33- and 34-plated sticklebacks were favored during 1971 in basin 1 and basin 2, respectively, and 28-to 29-plated individuals were favored in both basins in 1972. Asymmetrical disruptive selection favored individuals with extreme phenotypes within the p a r t i a l l y plated morph in 1971. In 1972, the pattern of fitnesses of phenotypes within this morph were similar to that in basin 1 in both 1971 and 1972. Disruptive selection favoring individuals with extreme phenotypes acted within a l l morphs. This suggests a relationship between the frequency of a phenotype i n the population and the chances for an individual with that phenotype to survive from May to September. The most frequent 38 FIG. 11: Relative fitness of plate number phenotypes within morphs from May to September, 1971 (0) and 1972 (©) in basin 2. P L A T E N U M B E R U ) C O 0 ) 39 phenotypes within a morph were never the optimum phenotype, and often had the lowest fitness. Disruptive selection could be due to environmental heterogeneity i n either space (differences between areas) or time (changes from May to September). (2) Changes in frequencies of plate number phenotypes from year to year. Frequencies of plate number phenotypes within morphs in May of 1971» 1972, and 1973 were compared to determine i f frequencies change from year to year. Frequencies of phenotypes within the low and completely plated morphs changed from year to year in both basins (Table X). Relative frequencies of p a r t i a l l y plated phenotypes changed from year to year i n basin 2, but did not change significantly between years in basin 1. Relative change in frequency was calculated for each phenotype. to examine patterns of change in frequencies of plate phenotypes between years. The phenotype within a morph with the greatest increase i n frequency from one year to the next was given a value of 1, and other phenotypes were compared to this "optimum" phenotype. Relative change in frequency fromyyear to year i s not relative fitness. Extreme plate numbers within the low plated morph decreased in frequency in basin. 1 from 1971 to 1972 (Fig. 12), and 8-plated sticklebacks were the optimum morph. Extreme phenotypes within this morph increased i n frequency from 1972 to 1973, while central phenotypes 40 FIG. 12: Relative change of frequency of plate number phenotypes within morphs from May in one year to May in the following year in basin 1. (0—0 1971-1972, 6—@ 1972-1973). > 1 i i 1 1 1 i 1 1 1 1 1 1 H 1 1 1 1 j 3-4 5 6 7 8 9-16 8-16 17-8 19-20 21-2 23-4 25-6 27-9 2£V9 30 31 32 33 345 P L A T E N U M B E R o 41 TABLE X: Summary of tests of homogeneity of frequencies of plate number phenotypes within morphs from May of one year to May i n the following year. BASIN YEARS PLATE MORPH 2 X Of. P 1 1971-1972 Low plated 37.31 5 < 0.005 P a r t i a l l y plated 2.96 6 > 0.75 Completely plated 19.74 5 < 0.005 1972-1973 Low plated 23.10 5 < 0.005 P a r t i a l l y plated 12.26 6 > 0.05 Completely plated 16.32 5 < 0.005 2 1971-1972 Low plated . 37.42 5 < 0.005 Partially plated 30.41 6 < 0.005 Completely plated 31.96 5 < 0.005 1972-1973 Low plated 29.03 5 < 0.005 P a r t i a l l y plated 32.76 6 < 0.005 Completely plated 32.15 5 < 0.005 1+2 decreased. An extreme phenotype within the completely plated morph was favored from both 1971 to 1972 and 1972 to 1973. The optimum pheno-type from 1971 to 1972 had 33 plates and 28-to 29-plated individuals showed the greatest decrease in frequency, but this pattern was reversed from 1972 to 1973, with 28-to 29-plated sticklebacks being favored and 33-?to 35-plated individuals decreasing in frequency. Patterns of change in frequency of phenotypes within the•partially plated morph were similar from 1971 to 1972 and 1972 to 1973, favoring 8-to l6-plated individuals while higher plate numbers decreased in frequency. In basin 2, extreme phenotypes were favored between years within a l l morphs (Fig. 13). Within the low and completely plated morphs the extreme phenotype that was favored from 1971 to. 1972 showed the greatest decrease in frequency from 1972 to 1973, and the other extreme phenotype showed the inverse pattern. Both extreme phenotypes within the p a r t i a l l y plated morph were favored from 1971 to 1972, and showed the greatest decrease in frequency from 1972 to 1973, when central phenotypes were favored. The favored phenotype between years within the low and completely plated morph were similar in both basins. From 1971 to 1972, 33-to 35-plated individuals were favored within the completely plated morph in both basins. From 1972 to 1973, 9-to l6-plated individuals were favored within the . low plated morph i n both basins. This suggests that factors causing changes in the frequency of plate number phenotypes from year to year were similar in both basins. 43 Sticklebacks with extreme phenotypes within the low and completely plated morphs were favored both within and between years in'-both basins. The optimum phenotype within these morphs from May to September of a year was also often favored from that year to the next, although the optimum phenotype switched from one extreme to the other in time. C. Summary I expected to find general trends i n the changes i n frequencies of phenotypes with time, perhaps similar to those observed i n changes in morph frequencies in basin 1. Clearly, such trends did not occur. The expectation resulted from an over-simplified view of the population structure, and arguments, based on that view, about --.the effect of increasing population size on genetic variation i n populations. The observed changes in phenotype frequencies lead to.several conclusions: (1) natural selection acts on variation in plate numbers, producing changes in relative frequency of phenotypes within generations. (2) frequencies of phenotypes also change from generation to generation, and changes within and between generations are related; (3) chances for an individual to survive and for i t s phenotype to increase in relative frequency in the next generation depend on interactions between i t s phenotype and the environment in space and time; (4) the selective environment for a stickleback i s clearly variable in both space and time. hk FIG. 13: Relative change of frequency of plate number phenotypes within morphs from May in one year to May i n the following year in basin 2. (0—0 1971-1972, $—® 1972-1973) > o LOW PLATED PARTIALLY PLATED COMPLETELY PLATED 1 1 1 1 1 1 1 1 T r 9-15 8-16 17-8 19-20 21-2 23-4 25-6 27-9 28-9 30 34-5 P L A T E N U M B E R 45 STICKLEBACKS AND SCHISTOCEPHALPS SOLIDUS Schistocephalus solidus i s a tapeworm found as a plerocercoid i n Gasterosteus aculeatus. The l i f e history of Schistocephalus follows the pattern? egg, free-swimming coracidium, procercoid in copepod, plero-cercoid i n f i s h , adult in piscivorous bird. Infection prevents normal egg maturation of female sticklebacks (Arme and Owen, 1Q67),reduces the chances of a male to build a nest (McPhail, pers. comm.), and increases the probability that an individual w i l l be eaten by birds, as infected sticklebacks are sluggish and found in shallow water (Lester, 1971). Since infection with Schistocephalus affects the chances for an individual to survive and reproduce, I was interested in determining i f d i f f e r e n t i a l infection of plate phenotypes might explain observed changes in frequencies of phenotypes with time. The proportion of infected sticklebacks changes within a year (Fig. 14). The rate of infection increased from May to August, and decreased from August to September in basin 2 during 1970. Samples of sticklebacks from basin 2 in June, 1970, suggested that differential infection of morphs occurred, even though differences between morphs were not significant. Large samples of sticklebacks were collected from a station in each basin (stations 11 and 18) during June, 1971, to test the hypothesis that morphs have different probabilities of becoming infected. Proportions of infected and uninfected sticklebacks of each morph were compared to determine i f morphs were d i f f e r e n t i a l l y infeoted. 46 FIG. 14: Rate of infection of sticklebacks with Schistocephalus solidus i n basin 2 during 1970. Numbers in brackets are the t o t a l number of sticklebacks caught. — lOOn 1 i 1 i 1 MAY JUNE JULY AUGUST SEPTEMBER M O N T H 47 The morphs were di f f e r e n t i a l l y infected in both basins (Table XI). In basin 1, the proportion of infected individuals was higher for the p a r t i a l l y plated morph than for the low and completely plated morphs. In basin 2, the proportion of infected sticklebacks was lower for the p a r t i a l l y plated morph than for the other morphs. Partia l l y plated sticklebacks decreased and low and completely plated individuals increased i n relative frequency both within and between years in basin 1. At station 18 i n basin 2, p a r t i a l l y plated individuals increased i n relative frequency during 1971 and from 1971 to 1972. This suggests that the selective environment for a stickleback varies in space, and that d i f f e r e n t i a l infection of morphs is at least part of the explanation for changes in the relative frequencies of phenotypes with time. Two hypotheses could explain the observed differences between morphs in rate of infection: (1) A l l morphs have the same probability of becoming infected, and differences between morphs in level of infection are ^ u e ^o d i f f e r e n t i a l survival of infected sticklebacks on the basis of phenotype. Two observations argue against this hypothesis: (a) few plerocercoids are mature during June, and therefore unlikely to cause mortality; (b) d i f f e r e n t i a l survival during the summer favors the morphs with the lowest infection rates rather than those with the highest infection rate, as this hypothesis requires. (2) the morphs have different probabilities of becoming infected. Sticklebacks become infected by eating copepods carrying a procercoid, and this hypothesis argues that the phenotype of an individual influences i t s 1 48 TABLE XI: Proportion of sticklebacks with different plate morphs infected with .Schistocephalns solidus i n Heisholt Lake, June 1971. Chi-squares are from test of associa-tion between infection rate and morphs in each basin. INFECTED PLATE MORPH .NUMBER NON-INFECTED NUMBER Low plated 15 17 P a r t i a l l y plated 27 27 Completely plated 6 10 Low plated 16 31 Part i a l l y plated 14 l4 Completely plated 29 28 75 74 53 X 2 = 7.17, 2d£, p<0.05 36 87 73 83 73 90 69 86 72 X 2 = 8.20, 2d£, p<0.025 49 chances to eat an infected copepod. Summary Morphs were di f f e r e n t i a l l y infected with Schistocephalus i n both basins during June: par t i a l l y plated sitcklebacks had the highest infection rate in basin 1 and the lowest infection rate in basin 2. Increased mortality of infected individuals would account for at least part of the change i n relative frequencies of morphs. MOVEMENTS OF STICKLEBACKS The observation that morph frequencies change from area to area within a basin led to a series of experiments on movements of sticklebacks in Heisholt Lake. These experiments involved releasing marked sticklebacks in the area where they were collected and following their movements for short periods. This section of the thesis presents results of these experiments. A. Movement Patterns In May and August, 1971, experiments were conducted to determine the pattern of movement of sticklebacks. Traps were set in an area at the base of a U-shaped bay (Fig. 15) for 24 hrs (Day 0). A l l sticklebacks i n the traps were then marked with a clipped spine, and released at the exact site they had been caught. Equal numbers of traps were set i n the release area and at distances of 5, 10, 15, and 20 m from this area. Traps were checked every 24 hrs for three days (Days 1-3), and the numbers of marked and unmarked sticklebacks i n each trap were recorded. Sticklebacks were always released where they had been caught, and the.traps were replaced at the same sites each day. , 50 In May, 299 marked sticklebacks were released in a bay in basin 2. The frequency of marked sticklebacks on Day 1 was highest in traps in the release area, and declined as the distance from the release area increased (Fig. l 6 ) . The frequency of marked sitcklebacks did not change from day to day in the release area, but i t decreased from Day 1 to Day 3 at 5, 10, and 15 m, and from Day 2 to Day 3 at 20 m from the release area. In August, 238 marked sticklebacks were released in a bay in basin 1. The pattern of change in frequency of marked sticklebacks from day to day was similar to that in May. Frequency of marked individuals did not change from day to day i n the release area, and declined during the experiment at a l l distances outside the release area. Results of these experiments suggest that the population i s composed of two groups of sticklebacks with very different patterns of movement: (1) a resident group that remains within a restricted area; (2) a non-resident group that moves from area to area. An experiment was conducted to examine patterns of movement of these two groups. In May, 1972, 332 sticklebacks were caught i n a U-shaped bay in basin 2, marked, and released at the site where they had been caught. Equal numbers of traps were set in the release area and at 5» 10, 15 and 20 m from this area. A second spine was clipped on a l l marked sticklebacks caught in traps on Day 1, but those caught in the release area (residents) were marked so that they could be distinguished from those caught outside the release area (non-residents). A l l double-marked sticklebacks were released at the same site in the release area.' 51 FIG. 15: Sketch of U-shaped bay (Station 26) in basin 2 used for experiment on movement patterns of sticklebacks, showing sites at which traps were set. 51a X TRAP SITE Frequency of marked sticklebacks at different distances from release area in May and September, 1971. D I S T A N C E FROM R E L E A S E A R E A (m. 53 Movement patterns of resident and non-resident sticklebacks were very different (Fig. IT). Most residents (86%) stayed i n the release area, whole most non-residents (83%)-moved. While this result supports the hypothesis that the population is composed of two groups with different movement patterns, i t also raises questions about why the frequency of marked individuals did not decline from day to day in the release area daring previous experiments, since this experiment suggests that some of the marked individuals caught in the release area on Day 1 were actually non-residents. Several hypotheses would explain differences between individuals i n movement patterns. Breeding sticklebacks do not leave the release area, suggesting that they are residents. T e r r i t o r i a l i t y of breeding sticklebacks would explain differences i n movement patterns i n May, but not i n September. Larson (1972) dhowed that sticklebacks maintain feeding t e r r i t o r i e s , and t e r r i t o r i a l behavior was observed throughout the summer in Heisholt Lake. A combination of breeding and feeding t e r r i t o r i e s would explain behavioral differences between residents and non-residents. B. Relative Numbers of Residents and Non-Residents Frequency of marked sticklebacks in the release area was higher i n May than in August. This difference can be explained by two alternative hypotheses: (1) relative numbers of residents and non-residents did not change from May to August, but a lower proportion of residents i n the release area were marked in May, when density of sticklebacks was higher; (2) relative numbers of residents and non-residents change, so that more sticklebacks are residents during August. 54 FIG. 17: Movement of resident and non-resident sticklebacks from release area in May, 1972. • 54a DISTANCE FROM RELEASE AREA ( m.) 55 The f i r s t hypothesis argues that, i f I continue to mark sticklebacks in the release area in May, the frequency of marked individuals vould increase from day to day as more residents became marked. To test this prediction, I set ten traps i n a bay in basin 2 in May, 1972, and a l l sticklebacks in the traps were marked the next day, and released. The traps were replaced at the same sites and checked each day for three days. The numbers of marked and unmarked sticklebacks were recorded each day and a l l unmarked sticklebacks were marked. Frequency of marked individuals did not i n -c E e a s e from day to day (Table XII) suggesting that most residents i n the area had been caught and marked on the f i r s t day. This result supports the hypothesis that changes in the relative numbers of resident and non-resident sitcklebacks explain differences between experiments in May and September. Changes in the relative frequency of resident and non-resident sticklebacks from May to September suggest a relationship between density of sticklebacks and the proportion of sticklebacks in the population that obtains a territory and becomes resident. Several mark-recapture experiments were conducted during 1972 and 1973 to examine this relationship (Appendix D). Fig. 18 summarizes a l l observations on the relationship between density (number of sticklebacks per trap) in the release area and the frequency of marked sticklebacks in the release area on Day. 1. The proportion of the population that obtains a territory and becomes resident appears to decrease as stickleback density increases. However, the relationship is confounded by seasonal changes in behavior, as breeding and feeding t e r r i t o r i e s are not the same. This hypothesis requires further testing before a conclusion can be made. 56 TABLE XII: Frequencies of marked and unmarked sticklebacks in an area in basin 2 in May, 1972. NUMBER OF STICKLEBACKS FREQUENCY OF MARKED .UNMARKED MARKED STICKLEBACKS {%) 0 U03 65 287 18.5 77 349 18.1 78.. 303 20.5 57 C. Summary The stickleback population in Heisholt Lake is composed of resident individuals, which maintain either a feeding or a breeding ter r i t o r y , and non-resident individuals, which move rapidly from area to area. The proportion of sticklebacks that obtain terr i t o r i e s appears to decrease as population density increased. VARIATION OF RESIDENT AND NON-RESIDENT. STICKLEBACKS Experiments on movement patterns of sticklebacks in Heisholt Lake show that the population is composed of residents, which remain in a restricted area, and non-residents, which move from area to area. Only resident sticklebacks breed, and the proportion of sticklebacks with te r r i t o r i e s appears to decrease with population density. These observations argue that sticklebacks compete for t e r r i t o r i e s , and the change in frequencies of phenotypes from area to area suggest that the plate phenotype of an individual influences i t s chance of becoming a resident i n an area. Plate phenotypes of resident and non-resident sticklebacks were compared to determine i f a l l phenotypes had equal probabilities of becoming a resident. I asked t h r e e q u e s t i o n s : (1) does the plate phenotype of a male affect his chances of obtaining a breeding territory? (2) does the plate phenotype of a female affect her chances of breeding? (3) does the plate phenotype of an individual affect i t s chances of obtaining a feeding territory, and thus becoming a resident outside 58 FIG. 18: The relationship between density of sticklebacks (catch/unit effort) in release area on day 1 and the proportion of sticklebacks with terr i t o r i e s (frequency of marked sticklebacks i n release area) i n release area on day 1. b£ u CD UJ _I O STl < Q UJ UJ < DC < UJ 2 AS u_ UJ O EL >- or u z 1 • 1 z D o UJ or 50-i 40H 3CH 20H © O i— I O 20 30 40 ~50 C A T C H / U N I T E F F O R T 59 the breeding season? This section of the thesis presents results of comparisons of the phenotypes of resident and non-resident sticklebacks, A. Nesting Males Nesting males were collected at five stations i n basin 1 each year from 1971 to 1973, and at five stations in basin 2 i n 1973. A l l nests at a station were collected within 36 hours during mid-May. Territories vacated by removal of a male were usually reoccupied within 2k hr. Morph frequencies of males collected at a station during early May and morph frequencies of males nesting at the same station were used to calculate relative fitnesses of morphs. Relative fitnesses of morphs were compared to determine i f the phenotype of a male affects his chances of obtaining a breeding territory (Table XIII). In basin 1, p a r t i a l l y plated males had the lowest chances of obtaining a territory at a l l stations i n a l l years. The favored phenotype varied from station to station i n 1971 and 1972, but completely plated males had the highest fitness at a l l stations in 1973. In basin 2, the favored morph varied greatly between stations (Table XEV). P a r t i a l l y plated males had a selective advantage at station 30, but they also had the lowest fitness at three of the five stations. Morph frequencies of nesting males at a l l stations in a basin were compared to determine i f the. phenotypes of nesting males varied in space. Differences between stations in basin 1 were not significant i n either 1971, 1972, or 1973 (Table XV), but morph frequencies of nesting males varied between stations in basin 2 i n 1973. TABLE XIII: Relative fitness of marks with different plate morphs "breeding in basin 1. 1971 1972 1973 STATION MORPH SAMPLE MALES NESTING MALES RELATIVE FITNESS SAMPLE MALES NESTING MALES RELATIVE FITNESS SAMPLE MALES NESTING MALES RELATIVE FITNESS 2 Low plated 23 12 1 46 10 1 33 9 0.57 Partially plated 20 3 0.29 42 7 0.77 24 3 0.26 Completely plated 16 4 0.48 36 7 0.89 29 14 1 5 Low plated. 6 7 0.58 32 22 0.90 28 7 0.31 Partially plated 14 9 0.32 31 10 0.42 29 - 7 0.30 Completely plated 6 12 1 21 16 1 21 17 1 7 Low plated 14 8 0.57 15 11 , 0.73 24 10 0.46 Partially plated 5 0 0 20 5 0.25 19 5 0.29 Completely plated 4 4 1 9 9 1 11 10 1 9 Low plated • 15 14 0.39 20 6 0.21 42 11 l P a rtially plated 9 6 0.36 28 . 5 0.13 26 4 0.58 Completely plated 5 12 1 10 14 1 38 10 1 11 Low plated 27 14 1 43 12 0.50 bl 9 0.65 Partially plated 31 .4 0.25 25 4 0.28 33 6 0.62 Completely plated 26 13 0.96 32 18 1 34 10 1 . o 61 STATION 19 23 TABLE XIV: Relative fitness of males with different plate morphs breeding in basin 2, 1973. PLATE MORPH Low plated Parti a l l y plated Completely plated Low plated Pa r t i a l l y plated Completely plated SAMPLE MALES 5 13 9 10 18 8 NESTING MALES 7 11 8 11 6 18 RELATIVE FITNESS 1 0.60 0.63 0.49 0.15 l :. 25 Low plated P a r t i a l l y plated Completely plated 11 12 8 13 11 7 1 0.78 0.71+ 27 Low plated Pa r t i a l l y plated Completely plated 12 15 6 12: 11 5 1 0.73 0.83 30 Low plated Pa r t i a l l y plated Completely plated 31 28 18 11 12 3 0.83 1 0.39 TABLE XV: Summary of tests of homogeneity of morph frequencies of nesting males at different stations. 1971 8.76 6 > 0.25 1972 8.74 8 > 0.25 1973 5.03 8 > 0.75 1973 17.11 8 <0.05 These results show that the plate phenotype of a male influences his chances of obtaining a breeding territory i n a particular area, and that the selective environment for males varies i n space. B. Breeding Females The breeding condition of female sticklebacks collected during May from 1971 to 1973 was recorded. Plate phenotypes of breeding and non-breeding females were compared to determine i f a l l phenotypes .have an equal chance of breeding. I assumed that, i f a female had ripe eggs, she would breed. Numbers of females breeding at a station were small, so a l l collec-tions from a basin were combined. Differential breeding of morphs occurred within both basins in 1971 and 1972, but differences between morphs were not significant i n 1973 in either basin 1 or basin 2 (Table XVI). Par t i a l l y plated females were selected against in a l l years in basin 1 (Table XVII). Low plated females were favored in 1971 and 1972, and completely plated females were favored in 1973. In basin 2, p a r t i a l l y plated females were favored i n 1971 and 1973, and completely plated females ahd the highest relative fitness in 1972. Low plated females were selected against i n basin 2 i n a l l years. Relative fitnesses of plate number phenotypes within morphs were calculated to determine i f plate number affects the chances for females of a particular morph to breed (Appendix E). Disruptive selection favored extreme phenotypes of the completely plated morph in 1972 and 1973 (Fig. 19). Directional selection favored an extreme phenotype of the completely plated morph in 1971. The type of selection changed from year to year within the part i a l l y plated morph, as selection was stabilizing in 1971, and disruptive, TABLE XVI: Summary of tests of association between the plate morph of female sticklebacks and breeding condition. DATE BASIN X. 2 1971 1 7.30 < 0.025 2 13.86 < 0.005 1972 1 6.26 < 0.05 2 20.12 < 0.005 1973 . 1 3.03 > 0.10 2 0.91 > 0.50 TABLE XVII: Morph.frequencies of breeding and non-breeding female sticklebacks and relative fitness of morphs in early May i n Heisholt Lake, 1971-1973. 1971 1972 1973 PLATE NUMBER OF FEMALES RF NUMBER OF FEMALES RF NUMBER OF FEMALES • RF BASIN MORPH BREEDING NON-BREEDING BREEDING NON-BREEDING BREEDING NON-BREEDING 1 Low plated 146 175 1 183 128 1 378 161 0.93 Partially plated 105 176 0.79 150 151 0.85 185 80 . 0.93 Completely plated 54 99 0.78 77 79 0 .84 226 74 1 2 Low plated 61 66 0.95 66 121 0.62 95 146 0.91 Partially plated 97 95 1 136 250 0.62 118 153 1 ' Completely plated 55 116 0.64 73 56 1 ' 73 100 0.97 1 66 FIG. 19: Relative fitness of plate phenotypes of female sticklebacks in basin 1. Fitness is defined in terms of chances to breed (Appendix E). LOW PLATED PARTIALLY PLATED COMPLETELY PLATED L L LU 0-5H 0-4 < 0-3 LU o-2-l en O-i-l o 3-4 6 8 9-16 8-16 17-8 19-20 21-2 23-4 25-6 27-9 28-9 3 0 31 3 2 33-5 P L A T E N U M B E R O N O N 0 ) 67 favoring an extreme phenotype, in 1973. In basin 2, disruptive selection favored extreme phenotypes within the low plated morph in 1972 and 1973, and within the completely plated morph in a l l years (Fig. 20). Selection was also of the disruptive type in a l l years within the par t i a l l y plated morph, but extreme phenotypes were not always favored. The disruptive pattern of selection within a l l morphs i n both basins suggests that the chances for a female to breed are influenced by the relative frequency of her plate phenotype in the population. Phenotypes within a morph with relatively low frequencies have a greater chance of breedin Density also appears to influence the relative chances for females of a particular phenotype to breed. The relative frequency of p a r t i a l l y plated females in the breeding group at each site in basin 1 during 1972 appeared to decrease as density of sticklebacks at the site increased (Fig. 21). This result suggests that pa r t i a l l y plated females had a lower probability of breeding as density increased, but this conclusion must be considered tentative as this relationship was not observed in either 1971 or 1973. The plate phenotype of a female stickleback influences her chances of breeding. The selective environment for females varies in space (differences between basins) and time (differences between years). 68 FIG. 20: Relative fitness of plate phenotypes of female sticklebacks in basin 2. Fitness i s defined in terms of chances to breed (Appendix E). R E L A T I V E F I T N E S S m ^89 69 FIG. 21: The relationship between density of sticklebacks i n a trap and the relative frequency of the p a r t i a l l y plated morph in the breeding females caught in the trap, 1972. 69a O O - i 8CH 60H < 4 0 - ® 20H e ® 9 9 9 —I r® ® l 9 1 © — | — 2 0 4 0 6 0 S O I O O 1 2 0 1 4 0 C A T C H / U N I T E F F O R T ( S T I C K L E B A C K S / T R A P ) TO C. Residents and Non-residents in September A mark-recapture experiment was conducted during September, 19T2, to compare the plate phenotypes 6'f resident and non-resident sticklebacks outside the breeding periods. Traps were set for 2k hours in a bay of basin 1, and 423_ sticklebacks were caught and released. Equal numbers of traps were set in the release area and at 5, 10, 15, and 20 m from the release area. The traps were checked for the next three days, and a l l marked individuals caught in the release area (residents) and outside the release area (non-residents) were compared to determine i f the phenotype of an individual influenced i t s chances of obtaining a feeding territory (Table XVIII). Morph frequencies of resident and non-resident sticklebacks were significantly different (chi-square t e s t , x 2 = 10.T8; 2 d.f., p>0.0l). Partia l l y plated sticklebacks were more frequent i n the non-resident group than in the resident group, completely plated sticklebacks were more frequent in the resident group, and the frequency of low plated individuals was similar in both groups This shows that the plate phenotype of a stickleback i n -fluenced i t s chances of obtaining a feeding territory, and that low and completely plated sticklebacks had an advantage over p a r t i a l l y plated sticklebacks in obtaining a feeding territory in an area of basin 1. D, Summary Clearly, the plate phenotype of a stickleback influences i t s chances of TABLE XVIII: Morph frequencies of resident and non-resident sticklebacks in basin 1, in August, 1972. Chi-square is from test of association between morph and movement pattern.:. LOW PLATED NUMBER PARTIALLY PLATED NUMBER % COMPLETELY PLATED NUMBER % Residents 27 47 Non-residents 40 50 6 10 23 29 25 17 43 21 X 2 = 10.78, 2df, p>0.01. • 72 obtaining a territory both during and after the breeding season. In basin 1, low and completely plated sticklebacks had a selective advantage over pa r t i a l l y plated sticklebacks in obtaining a breeding territory in a l l years. Low and completely plated sticklebacks were also favored over par t i a l l y plated individuals in obtaining a feeding territory. In basin 2, the favored morph varied from area to area and from year to year. Parti a l l y plated males were favored in certain areas and p a r t i a l l y plated females had a selective advantage in 1971 and 1973. In both basins, disruptive selection favored extreme female phenotypes withinall morphs during the breeding season. 73 SUMMARY OF RESULTS I was interested in the adaptive significance and maintenance of variation in plate number in threespine sticklebacks. My approach in the study was: (1) to describe spatial and temporal changes in the frequencies of plate phenotypes in Heisholt Lake; (2) to attempt to explain observed changes. This section of the thesis presents a summary of the results of the study. A. Changes in the Frequency of Phenotypes Spatial and temporal changes in phenotypic frequencies were observed in Heisholt Lake. Morph frequencies changarfwith depth during June owing to segregation of breeding females, which suggests that the morphs differ physiologically. Morph frequencies also changq^from area to area within a basin. Changes in phenotypic frequencies occurred both within generations (from May to September) and between generations (from year to year). In basin 1, low and completely plated sticklebacks increased and p a r t i a l l y plated sticklebacks decreased in frequency both within and between generations at most stations. In basin 2, p a r t i a l l y plated sticklebacks increased and low and completely plated sticklebacks decreased in frequency at many stations in both 1971 and 1972, and at most stations from 1971 to 1972. However, from 1972 to 1973 this pattern was reversed. Extreme phenotypes within a l l morphs increased in frequency both within and between generations i n both basins. Disruptive selection favoring both extreme phenotypes within generations occurred within a l l morphs. B. Explanation of Observed Changes The observed changes in phenotypic frequencies in space and time in Heisholt Lake result from interactions between genetic variation and structure of the stickleback population. A series of experiments designed to determine the pattern of movement of sticklebacks in the lake show that the population is composed of resident individuals, which appear to maintain either a feeding or a breeding territory and remain in a restricted area, and non-residents, which move rapidly from area to area. Non-resident sticklebacks do not breed. The phenotype of an individual influences i t s chances of becoming a resident (i.e. to obtain a territory). In basin 1, low and completely plated sticklebacks had a selective advantage over p a r t i a l l y plated stickle-backs in becoming a resident both during and after the breeding season. In basin 2, p a r t i a l l y plated males were favored at some stations during the breeding season, and p a r t i a l l y platdd females had the greatest chance of breeding in both 1971 and 1973. Females with extreme phenotypes within morphs had the highest chances of breeding in both basins, and disruptive selection often favored both extreme phenotypes within a morph. The phenotype of a stickleback also influences i t s chances of being infected with Schistocephalus solidus during June. Parti a l l y plated sticklebacks had the highest infection rate in basin 2. A hypothesis to explain the observed differences in infection rate i s that the morphs differ in their probability of becoming infected because of differences in feeding behavior. 75 t Although population size increased each year during the study, density of sticklebacks was not a major factor influencing the observed spatial and temporal changes in phenotypic frequencies. Spatial changes in phenotypic^ are a result of variation i n space of the outcome of competition among phenotypes for t e r r i t o r i e s . Physiological differences •••between phenotypes may be a factor in this competition. Temporal changes i n phenotypic frequencies are also explained by interactions between genetic variation and population structure, as phenotypes that are favored in competition for terr i t o r i e s have the lowest rate of infection with Schistocephalus, and increase i n frequency both within and between generations. Differences in survival rates of resident and non-resident individuals, owing par t i a l l y to differences in infection rate, would explain the observed changes in phenotypic frequencies within generations. Changes in the phenotypic frequencies between generations are explained by observed differences between phenotypes in chances of breeding. DISCUSSION A. Behavior and Movements of Sticklebacks Experiments on the movement patterns of sticklebacks in Heisholt Lake show that the adult population i s composed of a t e r r i t o r i a l resident group and a non-resident group that moves from area to area. Residents maintain either a feeding or a breeding territory. 76 Differences between individuals i n a population in patterns of movement are documented with other species of f i s h , particularly juvenile salmonids (Chapman and Bjornn, 1969; Jenkins, 1969; Symons, 1972), and with a variety of other vertebrates (Myers and Krebs, 1971; Watson and Moss, 1972). Complex social groupings within juvenile salmonid populations include'*dominant and subordiate t e r r i t o r i a l individuals; 'station-fish', who remain i n an area but do not defend i t ; and wanderers, who move from place to place (Symons , 1972). Van den Assem (1967) shows that complex social hierarchies exist between male sticklebacks with adjacent breeding t e r r i t o r i e s , and that courtship success i s influenced by social rank. The non-residents in Heisholt Lake may be individuals at the bottom of a complex social hierarchy. Rank in this hierarchy may determine the chances for an individual to survive and repro-duce. Possession of a territory confers numerous selective advantages: (1) growth rates of t e r r i t o r i a l f i s h are higher (Mason, 1969; Symons, 1970, 1972); (2) t e r r i t o r i a l f i s h have a lower probability of being eaten by a predator because of familiarity with an area (Jenkins, 1969; Symons, 1972); (3) t e r r i t o r i a l behavior of males reduces interference during breeding (van den Assem, 1967; Bartnik, 197$); (k) t e r r i t o r i a l f i s h have an advantage in feeding i n a familiar area (Bartnik, 1973)-Larson (1972) studied feeding behavior of two forms of sticklebacks that occur in Paxton lake on Texada Island. Pairs of sticklebacks were placed in tanks, and in every case one fish became dominant and the other became subordinate and moved away from the bottom of the tank. Preliminary 77 laboratory observations show that dominant-subordinate relationships occur within other stickleback populations, and that dominant individuals grow faster than subordinates (McPhail, per. comm.). This argues that growth rates are higher for resident individuals than for non-residents in Heisholt Lake. Observations of nesting males in Heisholt Lake suggest that behavior changes during a breeding cycle. Males are almost colorless and hide in a crevice or in vegetation during the early stages of the cycle, but later they become highly colored and are more active. Kynard (1972) shows that the response of breeding males to predators changes during the cycle. Males flee from a predator early in the cycle, but later they approach the predator. A hiding place w i l l reduce chances of being eaten by a predator, and rate of predation w i l l be lower for resident sticklebacks than for non-residents. The resident group during the breeding season includes breeding males and females, and perhaps non-reproductive individuals with feeding t e r r i t o r i e s . Long-term movement patterns of reproductive males and females probably d i f f e r . Breeding males establish t e r r i t o r i e s i n late A p r i l , build nests, court females, and guard eggs and young u n t i l their progeny are free-swimming. Males can go through this sequence at least twice, and may move their nest site between sequences (Black, 1972; Kynard, 1972). Both solitary and synchronous groups of nesting males were observed in Heisholt Lake. Females establish residence in an area, and may have several clutches of eggs before moving. Groups of synchronous males may be more attractive to females than solitary males (van den Assem, 1967; Bartnik, 1974). 78 During this study I observed that breeding females do not move from area to area. Laboratory observations suggest that females maintain 'feeding t e r r i t o r i e s ' , or at least w i l l be come .-dominant over another stickleback. Morris (1958) described t e r r i t o r i a l i t y of breeding females i n nine-spined sticklebacks, Pungitius pungitius, but such behavior has not been recorded for three-spined sticklebacks. This apparent con-tradiction may be resolved by comparisons of pelagic feeding populations, which tend to breed i n the open, and benthic feeding populations, which tend to breed in vegetation (Larson, 1972). Females in the former case may not be t e r r i t o r i a l in both Pungitius and Gasterosteus. Behavioral observations must not be made without an awareness of the ecological setting and genetic variation of the populations from which experimental individuals are collected. Non-resident sticklebacks are not solitary, but move rapidly in schools from area to area in Heisholt Lake. Keenleyside and Yamamoto (1962) reported that non-territorial salmon parr form schools at high densities and avoid terr i t o r y holders, thereby reducing the number of agonistic encounters. When a male stickleback is removed from his te r r i t o r y , another male, presumably a non-resident, usually occupies the territory within 2k hours. Territories become vacant in an area owing to movement of males and females that have either finished breeding or abandoned ter r i t o r i e s after f a i l i n g to breed, and, i f we assume that non-residents are searching for a vacant territory, the best strategy for non-residents is to move rapidly from area to area. 79 Hagen (1967) transferred marked sticklebacks from area to area in the L i t t l e Campbell River, and followed the movement of marked individuals. When low plated sticklebacks were transferred from a pond to a nearby-section of the river in March, numbers of marked fish at the release site decreased slowly, but upstream or downstream movement of marked sticklebacks was not apparent. Sticklebacks in Heisholt Lake do not move during March, but remain closely associated with the lake bottom. Hagen transferred low plated sticklebacks to a trachurus habitat and trachurus to a low plated habitat in June. In both experiments, sticklebacks moved away from the release area. Marked sticklebacks which are transferred between areas in Heisholt Lake move rapidly from the release area (Maclean, unpubl data). During summer and early f a l l , young-of-the-year sticklebacks move in large schools in shallow areas of Heisholt Lake. Young in laboratory tanks show no aggressive behavior during the same time period. In late f a l l , the young begin to fight, both in the lake and in the laboratory. The schools break up and the young sticklebacks settle in vegetation and crevices on the lake bottom. This fighting may determflntsocial rank and subsequent chances to survive and reproduce. Watson and Moss (1970) suggest that four conditions must hold in a population before we can conclude that behavior can limit breeding populations of sticklebacks. (l) a substantial part of the population does not breed. This study and van den Assem's (10-67). laboratory studfld indicate that only a certain number of sticklebacks can breed in a particular area. Also 2 a minimum territory size exists, and the number of non-territorial individuals appears to increase with density; 80 (2) such non-breeders are p h y s i o l o g i c a l l y capable of breeding i f dominant or t e r r i t o r i a l animals are removed. When male s t i c k l e b a c k s are removed from t h e i r nests i n the f i e l d , they are u s u a l l y r e p l a c e d w i t h i n 2k hours; (3) breeding animals are not completely u s i n g up some r e s o u r c e , such as food, space, or nest s i t e s . The area defended by a male s t i c k l e b a c k i s much l a r g e r than the nest s i t e . The number of males breeding i n an area i s g r e a t l y a f f e c t e d by s e t t l i n g p a t t e r n (van den Assem, 1967); (k) m o r t a l i t y or depressed recruitment due t o the l i m i t i n g f a c t o r changes i n an opposite sense t o , and at the same r a t e as, other causes of m o r t a l i t y or depressed r e c r u i t m e n t . Changes i n the numbers of s t i c k l e b a c k s i n H e i s h o l t Lake a f f e c t the r e l a t i v e numbers of r e s i d e n t and non-resident s t i c k l e b a c k s . Once t e r r i t o r i e s are f i l l e d , a d d i t i o n a l i n d i v i d u a l s become non-r e s i d e n t s . Vacant t e r r i t o r i e s are f i l l e d by non-residents. Behavior c l e a r l y l i m i t s the d e n s i t y of breeding s t i c k l e b a c k s i n a p a r t i c u l a r area at a p a r t i c u l a r t i m e , but may not l i m i t the t o t a l number of s t i c k l e b a c k s breeding i n the l a k e during a ye a r , as s e v e r a l breeding c y c l e s can occur w i t h i n an area d u r i n g a year. The p o p u l a t i o n s t r u c t u r e o u t l i n e d i n t h i s d i s c u s s i o n does not apply t o a l l s t i c k l e b a c k p o p u l a t i o n s . In some p o p u l a t i o n s , a d u l t s form l a r g e s c h o o l s , feed p e l a g i c a l l y (Moodie, 1972b), and h o l d t e r r i t o r i e s o n l y d u r i n g the breeding season. A comparative study of p o p u l a t i o n s t r u c t u r e would be most i n t e r e s t i n g . 81 B. Physiological Variation i n Gasterosteus acUleatus. During June, the phenotype of a "breeding female influences her distribution with depth in Heisholt Lake. Low and completely plated females are found at the shallowest and deepest depths respectively, while p a r t i a l l y plated females occur at a narrow, intermediate range of depths. Seasonal changes i n depth distribution of breeding females suggests that they cue on an environmental parameter, perhaps temperature, that changes seasonally at a given depth. Heuts (l94Ta) showed, that temperatures for optimal survival of eggs are higher for eggs from crosses between low plated males and females than for eggs from crosses between trachurus individuals. Females w i l l attempt to lay their eggs at optimal temperatures for survival, and differences i n the pre-ferred temperatures of females might explain differences between morphs in depth distribution. MacLean (1970) showed that preferred temperatures of five-spined sticklebacks (Culaea inconstans) are narrower during breeding than at other times of the year, and that normal breeding behavior occurs only within this narrow temperature range. Heuts (1947b) showed that the geographical distribution of low plated and trachurus sticklebacks is con-sistent with their physiological differences. Heuts (1945) found that optimal temperatures for survival of eggs from crosses between low-plated and trachurus sticklebacks are determined by the phenotype of the mother. Lindsey (1962) describes maternal effects on inheritance of vertebral number, a meristic character influenced by develop-mental temperature. However, the distribution of p a r t i a l l y plated females in Heisholt Lake suggests that they are physiologically intermediate. Hitzeroth, 82 et a l . (1968) show that maternal genes in trout hybrids are activated 40 days prior to activation of paternal genes at the same locus. Apparent maternal inheritance in sticklebacks might reflect differences in the temperature-dependent act i v i t i e s of products of maternal and paternal genes. Parti a l l y plated adults appear physiologically intermediate. The range of depths at which females are found is narrower for part i a l l y plated .'females than females of the other morphs. Bachmann (1969) reported that the temperature range for survival is narrower for hybrids between races of Rana pipiens than for parental populations. Temperatures for optimal survival of eggs may be narrower for eggs from p a r t i a l l y plated females than for eggs from females of the other morphs, and this hypothesis should be tested in the laboratory. Heuts (l94Ta) and Lindsey (1961) found physiological differences between plate number phenotypes within a morph. When low plated adults are placed in warm water, 3-4-plated individuals survive longer than those with seven plates. Temperatures for optimal survival of eggs are higher for 2-4-plated females than for females with seven plates. These results suggest that stickleback populations are composed of a, series of physiologically, and therefore ecologically, specialized phenotypes. Water temperatures in lakes and streams are extremely heterogeneous in space and time, and physiological variation i n sticklebacks permits them to survive and reproduce in a wide variety of habitats. .Recent studies show differences between plate phenotypes within morphs in nesting site (Moodie, 1972b; Kynard, 1972; Hay, 1974), in predator escape behavior (Moodie, McPhail and Hagen, 1973), and fecundity 83 (Kynard, 1972; Hay, 1974). Hagen (1972) suggests that plate numbers within morphs are inherited polygenically, but the pleiotropic interactions between plate number and a variety of characters influencing fitness of the individual suggest that inheritance of a plate number variation w i l l not be simple (see also Hay, 1974). The selective value of gene interactions, the degree of linkage, and the genes involved, i n the interacting complexes w i l l probably vary from population to population (Jones, 1973). C. Variation in Resident and Non-resident Sticklebacks Not a l l sticklebacks have equal chances of obtaining a territory in a particular area. The phenotype of an individual influences i t s chances to obtain a territory, and thereby i t s chances to survive and reproduce. In basin 1, low and completely plated sticklebacks had a selective advantage in acquiring a territory both dufjijng and after the breeding season. The low and completely plated morphs increased in relative frequency during the summer and from year to year. In basin 2, the morph favored in breeding varied from area to area and from year to year. In certain areas the p a r t i a l l y plated morph was favored, while i t was selected against throughout basin 1. The chances for an individual of a particular morph to survive from May to September also varied from area to area and from year to year in most areas. From 1971-1972, the pa r t i a l l y plated morph increased in frequency and the other morphs decreased, but this pattern was reversed from 1972-1973. Females with extreme plate numbers within the low and completely plated morphs had the greatest chance of acquiring a breeding territory. Low and completely plated sticklebacks with extreme plate counts increased in frequency from May to September and from year to year in both basins. These results show that a relationship exists between the relative a b i l i t y of individuals with a particular phenotype to successfully compete for a territory and the chances for individuals with that phenotype to survive and reproduce ( i . e . , increase in relative frequency within and between years). The selective environment influencing the fitness of phenotypes competing for territories„varies in space and time. Phenotype frequencies varied between areas at certain times in both basins. Movement of non-resident sticklebacks obscures differences in frequencies of phenotypes of residents from area to area, so significant differences are observed only when population density i s low and the selective environment influencing the phenotypes of individuals that acquire ter r i t o r i e s differs considerably between areas. Plate phenotypes were di f f e r e n t i a l l y infected with Schistocephalus in both basins. P a r t i a l l y plated sticklebacks had the highest infection rate in basin 1, and the lowest infection rate in basin 2. P a r t i a l l y plated sticklebacks were selected against in competition for t e r r i t o r i e s throughout basin 1, but i n some areas of basin 2, including the area where infection rate was examined, they were selected for. Differential infection of phenotypes can be explained by differences in the feeding behavior of resident and non-resident sticklebacks. T e r r i t o r i a l sticklebacks-feed predominantly on benthic organisms, while non-residents move away from the bottom and feed largely on plankton (Larson, 1972). Infection with Schistocephalus reduces the pro*-' bability of survival and reproduction, and may be a selective force causing changes in the frequencies of phenotypes with time. Disruptive selection favored females with extreme plate numbers within 85 morphs in both basins. Disruptive selection also favored extreme phenotypes in the low and completely plated morphs within years, and extreme pheno-types showed the greatest increase in frequency between years. These results suggest a relationship between frequency of a phenotype in the population and the a b i l i t y of individuals with that phenotype to compete successfully for t e r r i t o r i e s , which determines chances to survive and reproduce. Thoday (1972) concludes that disruptive selection occurs: (1) where heterogeneity of selection i s i n t r i n s i c to the biology of the population (sex dimorphism, etc.); (2) where heterogeneity of selection arises from environmental heterogeneity in space. Thoday suggests that maintenance of two or more optima may be dependent upon relative fitness being frequency-dependent. Roughgarden (1972) develops a model for evolution in populations in which individuals specialize on a specific region of a resource axis (where resources are arranged from small to large or from low to high along a single axis) present in the environment. The model predicts that there is an optimum number of individuals of each phenotype for a given set of resources, and that i f a population has this optimum distribution, then fitnesses of a l l phenotypes are equal. I f a sexual population i s to attain the optimum population distribution, the distribution of phenotypes in offspring from a given cross must have a certain shape, which w i l l be molded by natural section. This molding takes time, and the model predicts that when a population emigrates from a source with complex fauna, the variance of the offspring distribution w i l l result i n an overcrowding of the center phenotypes, which would result in 86 disruptive selection. This model has intriguing parallels with observations on the population of sticklebacks in Heisholt Lake. Plate phenotypes of sticklebacks appear to be specializing on a specific range of temperatures. Fitnesses of extreme plate numbers within morphs are higher than those of center phenotypes. The population is the result of a recent introduction of sticklebacks into an unoccupied lake. --A continuing study of plate variation in this population may reveal further parallels and since the source population i s known, may lead to further understanding of the adaptive significance and maintenence of plate variation. Also, the introduction of a predator, such as trout, into one of the basins would be an interesting experiment. Selander (19T0) also finds differences between areas in restricted populations of mice, but he invokes genetic d r i f t in small subdivided groups to explain changes from area to area. Numerous studies show, that isoenzyme variation is responsive to local conditions (Koehn and Rasmussen, 1967', O'Gower and Nicol, 1968; Johnson e_t a l . , 1969; Koehn, 1970; Prakash et a l . , 1969; Richmond, 1970; Marshall and Allard, 1970; Koehn et_ a l . , 1971; Smith and Koehn, 1971; Koehn and Mitton, 1972; Merritt, 1972; Williams et_ a l . , 1973). Myers and Krebs (1971) show that frequencies of certain genotypes are more common in dispersing Microtus pennsylvanicus than in residents. . In summary, spatial and temporal changes in the frequencies of plate phenotypes were observed in Heisholt Lake. Changes in both space and time result from selection acting on individuals competing for t e r r i t o r i e s . Differences between areas are caused by environmental heterogeneity in parameters affecting the chances for an individual with a particular phenotype of obtaining a territory. Changes of the frequency of a phenotype in time 87 are a result of the selective advantages of t e r r i t o r i a l sticklebacks i n terms of survival and reproduction. 88 BIBLIOGRAPHY Arme, C. , and R.W. Owen. 1967. Infections of the three-spined'stickleback, Gasterosteus aculeatus L., with the plerocercoid larvae of Schisto- cephalus solidus (Muller,. 1776), with special reference to pathological effects. Parasitology 57:301-314. 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Zool. 20:282-297-95 ' Stott, B. 196T- The movements and population densities of roach (Rutilus  rutilus (L)) and gudgeon' (Gobio gobio"(L)) in the River Mole. J. Anim. Ecol. 36:1+07-423. . 1970. Some factors affecting the catching power of unbaited fi s h traps. J. Fish Biol. 2:15-22. Symons, R.E.K. 19&9- The possible role of social and t e r r i t o r i a l behaviour of Atlantic salmon parr in the production of smolts. Tech. Rep. Fish. Res. Bd. Canada 206. 25p. Symons, P.E.K. 1972. Behavioural adjustment of population density to available food by juvenile Atlantic salmon. J. Anim. Ecol. 1+1:569-587. Thoday, J.M. 1972. Disruptive selection: A review. IProc. R. Soc. Lond. B. 182:109-11+3. Tinbergen, N. 1951. The study of instinct. Clarendon Press, Oxford. Van den Assem, J. 1967. Territory in the three-spined stickleback Gasterpsteus aculeatus L. Behaviour, Suppl 16: l64p. Watson, A. and R. Moss. 1970. Dominance, spacing behavior and aggression in relation to population regulation in vertebrates. In.: Animal Populations in Relation to Their Food Resources. A. Watson (ed). Bri t i s h Ecol. Soc. Symp. 10. Pp:l67-220. 96 Williams, G.C., R.K. Koehn, and J.B. Milton. 1973. Genetic differentiation without isolation in the American eel, Anguilla rostrata. Evolution 27: 192-204.. Wooton, R.J. 1972. The "behaviour of the male three-spined stickleback in a natural situation: a quantitative description. Behaviour 41:232-241. APPENDIX A: MORPH FREQUENCIES OF STICKLEBACKS IN HEISHOLT LAKE, 1971 - 1973. I i l MAY 1971 at i o n Low P l a t e d P a r t i a l l y P l a t e d Com1-P l a t e d TABLE A - I : Morph fr e q u e n c i e s of s t i c k l e b a c k s caught at 15 s t a t i o n s i n b a s i n 1 i n May and September from 1971-1973-NUMBERS OF STICKLEBACKS SEPTEMBER 1971 MAY 1972 SEPTEMBER 1972 MAY 1973 Low P a r t i a l l y Com-. Low P a r t i a l l y Com;-. Low . P a r t i a l l y Com- Low P a r t i a l l y P l a t e d P l a t e d p l e t e l y P l a t e d P l a t e d p l e t e l y P l a t e d P l a t e d p l a t e l y P l a t e d P l a t e d P l a t e d P l a t e d " '.".'.'Plated.'. 1 33 27, i6 i ' ! 22 8 14 4 6 38 30 22 7 . 16 18 10 i ; 2 35 18; • 37 28 3 2 89 63 4 8 3 0 14 27 19 9 u 3 49 hk 2 3 14 11 17 27 20 15 5 4 9 111 60 52 k 39 ' 28 23 : 37 1 0 3 0 47 28 "26 37 8 15 49 47 )•• 5 21 27 1 5 3 0 26 4 6 74 69 53 35 8 25 73 5 4 v 6 1 3 : 13 10 24 12 2 3 2 3 15 16 21 2 10 3 2 1 4 1( 7 58 13 45 28 61 4 2 4 8 34 44 0 27 83 53 8 58 i 39 28 30 26 32 4 2 25 1 3 39 9 34 . 65 32 3 o .. 38 I 33 1 4 31 18 37 38 43 25 4 6 18 25 112 54 r 10 >~. 0 ; 12 8 33 16 34 22 35 12 2 4 c; 54 36 11 82 ' ; 83 51 35 17 3 2 8 4 72 36 54 18 31 116 S~,_ • b? f 12 10 9 12 15 11 8 27 34 15 23 8 6 54 3 0 2 13 15 12 6 10 5 8 16 16 16 24 Q 12 ' 58 29" 14 56 ' 36 28 5 3 10 88 66 25 60 12 31 50 21 3 15 15 9 1 2 7 • 1 o 30 3 2 17 15 5 5 82 18 3 c4 TABLE A - I I : Morph frequencies o f s t i c k l e b a c k s caught at f i f t e e n s t a t i o n s i n b a s i n 2 i n May and September from 1971 - 1973. NUMBERS OF STICKLEBACKS MAY 1971 . SEPTEMBER 1971 MY 1972 SEPTEMBER 1972 MAY 1973 Lev P a r t i a l l y 00m- Low P a r t i a l l y Com- Low P a r t i a l l y Com- Low P a r t i a l l y Com- Low P a r t i a l l y Com-P l a t e d P l a t e d p l e t e l y P l a t e d P l a t e d p l e t e l y P l a t e d P l a t e d p l e t e l y P l a t e d P l a t e d p l e t e l y P l a t e d P i t t e d 7 pSt F l a t e d P l a t e d P l a t e d P l a t e d P l a t 16 3 0 kk 28 1 3 54 25 47 103 55 25 54 19 62 4 8 4 6 17 18 19 11 16 2 4 12 3 0 50 3 0 7 19 1 20 28 9 -1 r, ±C 18 20 19 7 21 10 2 3 53 27 10 3 1 13 44 52 2b 19 7 12 16 1 8 11 29 3k 21 18 28 10 15 22 14 20 17 33 15 23 3 9 26 40 83 44 20 34 21 4 1 60 49 21 7 13 14 18 29 15 26 61 36 - _ — 16 31 2 4 22 12' 10 6 17 22 21 16 42 4 14 21 10 20 2k 19 23 9 17 5 13 17 20 12 28 9 - - _ 27 3 1 15 24 1 4 13 11 11 21 10 26 52 26 2 10 5 31 2 3 3 1 2 5 9 17 15 6 9 7 22 51 34 8 7 7 20 51 26 10 Ik 13 14 16 7 10 3 1 1 4 5 5 4 27 32 15 27 7 15 17 14 25 11 20 22 13 11 18 1 1 21 3 0 15 28 2k 2 4 12 9 1 3 12 12 29 11 11 12 6 3 2 3 2 20 29 9 19 10 7 8 4 19 18 18 5 !.8 10 31 34 2 4 3 0 28 28 25 17 22 25 51 6 4 24 14 33 21 50 53 24 APPENDIX B: NUMBER OF STICKLEBACKS/TRAP IN HEISHOLT LAKE, 1970-1973. 101 YEAR MONTH BASIN NUMBER OF NUMBER OF CATCH/ STANDARD STICKLEBACKS TRAPS UNIT EFFORT DEVIATION 1970 May 1,2 364 34 10.7 11.1 September 1,2 289 82 3-5 6.4 1971 May 1 1249 73 17-1 22.2 2 734 39 18.8 12.5 September 1 999 77 13.0 15-9 ' . 2 732 113 6.5 4.9 1972 May 1 1680 56 30.0 23.2 2 1470 30 49.0 27.6 September 1 902 105 8.6 7-7 2 568 130 4.4 6.6 1973 May 1 2070 52 39.8 26.8 2 2506 39 64.3 27.1 September 1 187 113 1.7 3.5 2 344 115 3.0 4.9 1 102 APPENDIX C: FREQUENCIES OF PLATE NUMBER PHENOTYPES WITHIN MORPHS IN HEISHOLT LAKE, 1971-1973. TABLE C - I: Frequencies of plate number phenotypes within the low plated morph in basin 1. PLATE MAY 1971 SEPTEMBEE 1971 MAY 1972 SEPTEMBER 1972 ' MAY 1973 NUMBER NUMBER % NUMBER % . ...NUMBER: '-:.•%'•'•'.":'"•.• NUMBER % . NUMBER % 3 0 0 0 0 . 0 0 1 0 0 0 4 7 1 7 2 8 1 7 2 20 2 5 75 14 23 6 88 -13 38 8 132 13 6 190 36 115 31 224 32 126 26 311 32 7 186 35 110 29 299 43 167 35 352 36 8 29 5 47 13 63 9 61 13 105 11 9 8 1 15 4 5 1 30 6 23 2 10 4 1 17 5 3 0 12 3 12 1 11 4 l 5 1 1 0 13 4 8 1 12 6 l 0 0 1 0 7 1 1 0" 13 7 1 7 2 1 0 3 1 4 0 14 4 l 4 1 2 0 5 1 5 1 15 7 1 0 0 0 0 4 1 3 0 16 3 1 0 0 0 0 4 1 0 0 17 0 0 0 0 0 0 1 0 0 0 TABLE C - II: . Frequencies of plate number phenotypes within the pa r t i a l l y plated morph in basin 1. PLATE MAY 1971 SEPTEMBER 1971 MAY 1972 SEPTEMBER 1972 • MAY 1973 NUMBER NUMBER % NUMBER % NUMBER % . NUMBER % NUMBER , % 8 0 0 0 0 2 0 0 0 2 0 9 1 0 0 0 6 1 0 0 1 0 10 0 0 0 0 9 1 0 0 4 1 11 0 0 3 1 8 1 0 0 5 1 12 2 0 0 0 4 1 1 1 6 1 13 13 3 2 1 8 1 0 0 20 4 14 12 3 6 3 16 3 0 0 17 3 15 18 4 10 4 27 4 3 2 28 5 16 25 6 6 3 37 6 7 5 38 7 17 29 7 8 3 48 8 8 6 48 9 18 39 9 13 6 45 7 11 8 42 8 19 33 7 10 4 56 9 10 7 49 9 20 45 10 13 6 50 8 9 7 44 8 21 34 8 16 7 53 9 16 12 38 7 22 48 11 30 13 44 7 15 11 45 9 23 28 6 16 7 39 6 9 7 37 7 24 24 5 16 7 37 6 9 7 27 5 25 28 6 26 11 36 6 16 12 27 5 26 26 6 24 10 31 5 9 7 21 4 27 24 5 20 9 21 4 6 4 11 2 28 9 2 8 3 19 3 6 4 4 1 29 4 1 4- 2 8 l 0 0 4 1 TABLE C - III: Frequencies of plate number phenotypes within the completely plated morph in basin 1. PLATE MAY 1971 SEPTEMBER 1971 MAY 1972 SEPTEMBER 1972 • MAY 1973 NUMBER NUMBER % ' NUMBER % NUMBER % NUMBER % NUMBER % 28 0 0 0 0 0 0 0 0 3 29 19 7 19 5 8 2 11 k 3 1 5 3 0 69 25 104 26 75 20 65 2 3 1H8 26 3 1 81 29 113 29 108 28 75 26 158 27 3 2 80 29 103 26 117 31 84 29 148 26 3 3 23 8 47 12 62 16 kk 15 75 1 3 3 4 4 1 6 2 11 3 7 3 10 3 5 1 0 1 0 0 0 2 1 3 1 TABLE C - IV: Frequencies of plate number phenotypes within the low plated morph in basin 2. PLATE NUMBER 3 4 5 6 7 8 9 10 11 12 13 14 15 MAY .1971 SEPTEMBER 1971 NUMBER 0 17 53 74 37 7 5 2 6 4 3 5 6 T o 8 24 34 17 3 2 1 3 2 1 2 3 NUMBER 1 22 52 66 29 10 1 0 1 1 3 0 0 T I 12 28 30 16 5 1 0 1 1 2 0 0 MAY 1972 NUMBER 2 35 115 132 82 10 4 0 2 1 0 0 0 SEPTEMBER 1972 % 1 9 30 34 21 3 1-0 1 0 0 0 0 NUMBER 2 17 40 • 49 36 5 1 0 0 0 0 0 0 ol 1 11 27 33 24 3 0 0 0 0 0 0 0 MAY 1973 NUMBER 2 19 89 177 136 19 8 5 3 2 1 0 0 0 4 20 39 30 4 2 1 1 0 0 0 0 G TABLE C - V: Frequencies of plate number phenotypes within the partially plated morph in basin 2. MAY 1971 SEPTEMBER 1971 MAY 1972 ' SEPTEMBER 1972 MAY 1973 rliAiilj ^ NUMBER NUMBER. ~~i NUMBER. Jo NUMBER % • NUMBER [ % NUMBER 7 0 0 0 0 1 0 0 0 0 0 8 0 0 1 0 5 1 3 1 1 0 9 0 0 2 1 6 1 6 2 1 0 10 1 0 1 21 3 7 3 10 2 11 3 1 5 2 22 3 9 3 10 2 12 10 3 8 2 26 » 4 9 3 23 4 13 16 5 16 5 38 5 10 4 29 5 Ik 8 3 17 5 41 6 9 3 34 6 15 8 3 20 6 . 47 7 19 7 31 6 16 28 9 22 7 51 7 17 6 36 6 17 22 7 24 7 47 7 20 7 52 9 18 26 9 20 6 51 7 16 6 48 9 19 27 ' 9 20 6 43 6 12 44 8 20 20 7 20 6 47 7 15 5 38 7 21 29 10 18 5 39 5 17 6 42 8 22 17 6 18 5 31 4 19 7 40 7 23 17 6 15 5 42 6 11 4 28 5 2k 17 6 19 6 38 5 17 6 24 4 25 16 5 18 5 30 4 17 6 23 4 26 17 6 18 5 24 3 14 5 17 3 27 10 3 21 6 35 5 10 4 12 2 28 6 2 10 3 23 3 13 5 9 2 29 0 0 0 0 13 2 10 4 8 1 TABLE C - VI: Frequencies of plate number phenotypes within the completely plated morph in basin 2. PLATE MAY 1971 SEPTEMBER 1971 MAY 1972 SEPTEMBER 1972 MAY 1973 NUMBER NUMBER % NUMBER . % . . . NUMBER . . % NUMBER % NUMBER 28 1 0 0 0 0 0 0 0 0 0 29 13 6 23 11 2 1 . 2 1 17 5 30 41 19 6l 28 72 20 16 12 72 20 31 51 24 58 27 99 27 42 30 108 31 32 79 36 38 17 95 26 39 28 111 31 33 28 13 26 12 83 23 30 28 38 11 34 3 1 7 3 12 3 9 7 8 2 35 1 0 3 1 3 1 0 0 0 0 109 APPENDIX D: SUMMARY OF OBSERVATIONS ON THE RELATIONSHIP BETWEEN DENSITY OF STICKLEBACKS IN THE RELEASE AREA (CATCH/UNIT EFFORT) AND RELATIVE FREQUENCY OF RESIDENT STICKLEBACKS. 110 CATCH/UNIT EFFORT DATE (NUMBER STlCKLEBACKS/TRAP) IN RELEASE AREA May 1971 1+9.8 August 1971 17.0 May 1972 33.2 August 1972 • 26.5 May 1973 1+6.0 June 1973 1+6.5 FREQUENCY OF MARKED STICKLEBACKS IN RELEASE AREA ON DAY 1 {%) 16 1+1 26 1+5 13 15 1 111 APPENDIX E: PLATE NUMBERS OF BREEDING AND NON-BREEDING FEMALE STICKLEBACKS IN HEISHOLT LAKE IN MAY, 1971 - 1973. TABLE E - I: Plate numbers of breeding and non-breeding female sticklebacks of the low plated morph in Basin 1. NUMBER OF FEMALES P L A T E N U M B E R 1971 1972 BREEDING NON-BREEDING BREEDING • NON-BREEDING^ 1973 B R E E D I N G ::..:: N O N - B R E E D I N G : 4 2 2 3 1 11 0 5 18 27 26 16 59 14 6 51 66 55 44 92 63 7 47 62 75 57 127 72 8 9 8 19 8 52 7 9 2 2 1 0 15 -1 X 10 2 .2 2 0 5 0 11 2 1 0 0 3 2 12 2 2 2 0 2 1 13 4 0 0 0 7 0 14 3 0 0 2 5 1 15 3 2 0 0 0 0 16 1 1 0 0 0 0 TABLE E - I I 1971 I£2§ER BREEDING NON-BREEDING 9 0 0 10 0 0 11 0 0 12 0 2 13 4 5 14 2 ' T 15 li 7 16 7 12 IT - J 14 1.. 0 7 14 19 ' 9 20 SO 1> ' 12 ;:.! 14 19 8 14 .J 7 17 ?h 8 - 12 25 5 13 ?5 7 8 27 4 '•••8 4 P l a t e numbers of breeding and non-breeding female s t i c k l e b a c k s of the p a r t i a l l y u l a t e d morph i n b a s i n 1. • 1972' . BREEDING NON-BREEDING ' 'BREEDING EIVKJ-WEFH 0 l • l 0 2 .0 1 2 6 0 0 1 1 1 4 3 5 3 6 1 7 6 u 4 10 7 ' 10 7 8 20 20 7 13 11 • 19 15 12 19 7 11 11 15 ! 8 22 ' 16 15 11 . 18 ' 7 17 • 4 9 10 8 ...•.v.... 10 11 4 . 6 8 • 11 c 5 • • 5 10 9 3 6 0 5 3 j_ 0 4 1 0 TABLE E - III: Plate numbers of breeding and non-breeding female sticklebacks of the completely plated morph in basin 1. NUMBER OF FEMALES PLATE i2Ii 12Zi_ 19T3. NUMBER BREEDING NON-BREEDING BREEDING NON-BREEDING BREEDING NON-BREEDING 28 0 0 0 0 1 0 29 2 8 3 1 15 1 30 7 32 14 16 58 19. 31 20 26 19 23 54 25 32 17 25 20 28 51 26 33 7 7 19 10 40 3 34 l 1 2 1 7 0 TABLE E - IV: Plate numbers of breeding and non-breeding female sticklebacks of the low plated morph in basin 2. NUMBER OF FEMALES 1971 1972 1973 PLATE NUMBER BREEDING NON-BREEDING BREEDING NON-BREEDING BREEDING NON-BREEDING 3 0 0 1 0 1 0 4 5 6 8 11 5 3 5 15 13 10 43 11 27 6 23 22 29 43 38 6k 7 . 1 3 12 12 20 31 36 8 0 2 5 4 4 7 • 9 0 2 1 0 3 3 10 0 1 0 0 2 3 11 3 3 0 0 0 '2 12 1 1 0 0 0 1 13 0 3 0 0 0 . 0 Ik _ 0 0 0 0 0 0 15 1 1 0 0 0 0 TABLE E - V: P l a t e numbers of breeding and non-breeding female s t i c k l e b a c k s o f the p a r t i a l l y p l a t e d mor-oh i n "basin 2. PLATE NUMBER NUMBER OF FEMALES 1971 BREEDING NON-BREEDING 197! BREEDING NON-BREEDING L973 BREEDING NON-BREEDING 0 0 1 1 0 0 10 ;; ; :! . 0 1 5 7 i 5 : i • i 11 . j ' l " 0 0 5 7 2 1 ii 12 ;•>. 1 4 3 11 5 0 13 : 3 8 7 11 4 8 . : ' 5 0 8 12 9 6 15 6 8 9 0 u 4 9 7 9 9 18 2 12 !• 17 9 6 • 13 16 11 13 ! 18 5 11 8 23 12 12 1-19 9 7 11 22 12 • 13 ; 20 8 5 8 16 13 6 j 21 9 11 8 1* 12 16 22 6 6 5 13 ' 8 14 23 5 5 12 19 7 8 24 2 5 7 9 4 a 25 6 3 5 8 k 4 26 6 0 3 6 • k 3 27 T 1 6 6 16 l '4 28 3 0 2 10 3 2 29 0 0 1 2 0 2 TABLE E - VI: P l a t e numbers of breeding and non-breeding female s t i c k l e b a c k s of the completely p l a t e d morph i n b a s i n 2. • ' . ' ', ••• '/'/'/'/'''..'/'. NUMBER '/OF ' FEMALES . . / '  1971 . . 1972 1973 PLATE ' ' ' ' ' ~~J ' NUMBER BREEDING NON-BREEDING BREEDING NON-BREEDING ' BREEDING NON-BREEDING 29 1 1 6 3 8 i 30 8 28 15 12 7 30 31 8 36 16 16 17 38 32 12 33 23 20 31 2k 33 18 17 12 5 8 r O 3k 8 0 l 0 2 1 35 0 1 0 0 0 0 

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